Hey! Things are going well but I have a variable type mismatch that I haven't been able to figure out. The three statements are highlighted in red. I'm not done compiling but I got hung up there. The workbook is attached here New Formulation.xlsm Take a look and save me again?

Option Explicit
Option Base 1
Sub Coefficients()
Dim Rswrl As Double
Dim Lswrl As Double
Dim Ror As Double
Dim Alpha As Double
Dim rho_liq As Double
Dim visc As Double
Dim rho_air As Double
Dim surfT_liquid As Double
Dim Omega As Double
Dim Re As Double
Dim Ain As Double
Dim V1 As Double
Dim Ri As Double
Dim R As Double
Dim psi As Double
Dim psipsi As Double
Dim a As Double
Dim b As Double
Dim h As Double
Dim sum As Double
Dim First As Double
Dim Last As Double
Dim A1 As Double
Dim A2 As Double
Dim B1 As Double
Dim B2 As Double
Dim C2 As Double
Dim A3 As Double
Dim B3 As Double
Dim B33 As Double
Dim C3 As Double
Dim B4 As Double
Dim A4 As Double
Dim C(1 To 2, 1 To 2) As Double
Dim D(1 To 2, 1 To 1) As Variant
Dim C_inv As Variant
Dim F As Variant
Dim Zswrl As Double
Dim dz1 As Double
Dim K1 As Double
Dim K2 As Double
Dim K3 As Double
Dim K4 As Double
Dim L1 As Double
Dim L2 As Double
Dim L3 As Double
Dim L4 As Double
Dim F1 As Double
Dim F2 As Double
Dim Z1 As Double
Dim Z2 As Double
Dim Z3 As Double
Dim Z4 As Double
Dim Del1 As Variant
Dim Del2 As Double
Dim Del3 As Double
Dim Del4 As Double
Dim W1 As Variant
Dim W2 As Double
Dim W3 As Double
Dim W4 As Double
Dim Del1St As Variant
Dim W1St As Variant
Dim Pi As Double
Dim npts As Long
Dim k As Long
Dim Nswrl As Long
Dim IZ As Long
' Input Values:
' Geometry:
    Rswrl = ActiveSheet.Range("H18").Value / 2
    Lswrl = ActiveSheet.Range("H14").Value
    Ror = ActiveSheet.Range("H20").Value / 2
    Alpha = ActiveSheet.Range("H21").Value
    Ri = ActiveSheet.Range("H17").Value
' Properties:
    rho_liq = ActiveSheet.Range("H8").Value
    visc = ActiveSheet.Range("H9").Value
    rho_air = ActiveSheet.Range("H10").Value
    surfT_liquid = ActiveSheet.Range("H11").Value
' Preliminaries
    Pi = 3.14159265
    Ain = ActiveSheet.Range("H23").Value
    V1 = ActiveSheet.Range("H24").Value
' Swirl Chamber
'   Coefficients (constants - variable values must be added.
'    Coefficient A1
        npts = 20
        b = 1#
        a = 0#
        h = (b - a) / npts
    
'    First and Last Integration Points
        First = (2 * a - a ^ 2) - (2 * a - a ^ 2) ^ 2
        Last = (2 * b - b ^ 2) - (2 * b - b ^ 2) ^ 2
        sum = First
'    Odd terms
        For k = 1 To npts - 1 Step 2
            psi = 2 * k * h - (k * h) * (k * h)
            sum = sum + 4 * (psi - psi * psi)
        Next k
'    Even terms
        For k = 2 To npts - 1 Step 2
            psi = 2 * k * h - (k * h) * (k * h)
            sum = sum + 2 * (psi - psi * psi)
        Next k
 '   Add final value
        sum = sum + Last
        A1 = h / 3 * sum
        ActiveSheet.Range("R5") = A1
    
'    Coefficient A2
        npts = 20
        b = 1#
        a = 0#
        h = (b - a) / npts
'    First and Last Integration Points
        First = (2 * a - a ^ 2)
        Last = (2 * b - b ^ 2)
        sum = First
'    Odd terms
        For k = 1 To npts - 1 Step 2
            psi = 2 * k * h - (k * h) * (k * h)
            sum = sum + 4 * psi
        Next k
'    Even terms
        For k = 2 To npts - 1 Step 2
            psi = 2 * k * h - (k * h) * (k * h)
            sum = sum + 2 * psi
        Next k
 '   Add final value
        sum = sum + Last
        A2 = h / 3 * sum
        ActiveSheet.Range("R6") = A2
 
 '   Coefficient B1 and C2
        b = 1#
        a = 0#
        B1 = (2 - 2 * b) - (2 - 2 * a)
        ActiveSheet.Range("R7") = B1
        C2 = B1
        ActiveSheet.Range("R9") = C2
 
 '   Coefficient B2
        npts = 20
        b = 1#
        a = 0#
        h = (b - a) / npts
'    First and Last Integration Points
        First = (2 * a - a ^ 2) ^ 2
        Last = (2 * b - b ^ 2) ^ 2
        sum = First
'    Odd terms
        For k = 1 To npts - 1 Step 2
            psipsi = (2 * k * h - (k * h) * (k * h)) * (2 * k * h - (k * h) * (k * h))
            sum = sum + 4 * psipsi
        Next k
'    Even terms
        For k = 2 To npts - 1 Step 2
            psipsi = (2 * k * h - (k * h) * (k * h)) * (2 * k * h - (k * h) * (k * h))
            sum = sum + 2 * psipsi
        Next k
 '   Add final value
        sum = sum + Last
        B2 = h / 3 * sum
        ActiveSheet.Range("R8") = B2
        
' Zone 1
'       Circulation Constant
            Omega = V1 * (Rswrl - Ri)
'       Reynolds Number
            Re = Omega / visc
'       Initial value
            W1 = 0.001
            Del1 = 0.001
            Z1 = 0
'       Swirl Chamber Height
            Zswrl = ActiveSheet.Range("H18").Value
'       Number of Steps in Swirl Chamber Height
            Nswrl = 20
'           Delta-Z
            dz1 = Zswrl / Nswrl
        For IZ = 1 To Nswrl
'       Swirl Chamber Coefficient Matrix
            C(1, 1) = Del1 * W1
            C(1, 2) = Del1 ^ 2
            C(2, 1) = ((A2 - B2) * Del1 * W1 ^ 2)
            C(2, 2) = ((A2 - 2 * B2 + 1) * Del1 ^ 2 * W1)
            D(1, 1) = B1 / A1
            D(2, 1) = C2 * W1
        
'   Vector F Initial Conditions
            F = WorksheetFunction.MMult(WorksheetFunction.MInverse(C), D)
            ActiveSheet.Range("Y5") = F(1, 1)
            ActiveSheet.Range("Y6") = F(2, 1)
            F1 = F(1, 1)
            F2 = F(2, 1)
            K1 = dz1 * F1
            L1 = dz1 * F2
            Z1 = Z1 + dz1 / 2
            Del1 = Del1 + K1 / 2
            W1 = W1 + L1 / 2
            C(1, 1) = Del1 * W1
            C(1, 2) = Del1 ^ 2
            C(2, 1) = ((A2 - B2) * Del1 * W1 ^ 2)
            C(2, 2) = ((A2 - 2 * B2 + 1) * Del1 ^ 2 * W1)
            D(1, 1) = B1 / A1
            D(2, 1) = C2 * W1
            F = WorksheetFunction.MMult(WorksheetFunction.MInverse(C), D)
            F1 = F(1, 1)
            F2 = F(2, 1)
            K2 = dz1 * F1
            L2 = dz1 * F2
            Z2 = Z1 + dz1 / 2
            Del2 = Del1 + K2 / 2
            W2 = W1 + L2 / 2
            C(1, 1) = Del2 * W2
            C(1, 2) = Del2 ^ 2
            C(2, 1) = ((A2 - B2) * Del2 * W2 ^ 2)
            C(2, 2) = ((A2 - 2 * B2 + 1) * Del2 ^ 2 * W2)
            D(1, 1) = B1 / A1
            D(2, 1) = C2 * W2
            F = WorksheetFunction.MMult(WorksheetFunction.MInverse(C), D)
            F1 = F(1, 1)
            F2 = F(2, 1)
            K3 = dz1 * F1
            L3 = dz1 * F2
            Z3 = Z1 + dz1 / 2
            Del3 = Del1 + K2 / 2
            W3 = W1 + L2 / 2
            C(1, 1) = Del3 * W3
            C(1, 2) = Del3 ^ 2
            C(2, 1) = ((A2 - B2) * Del3 * W3 ^ 2)
            C(2, 2) = ((A2 - 2 * B2 + 1) * Del3 ^ 2 * W3)
            D(1, 1) = B1 / A1
            D(2, 1) = C2 * W3
            F = WorksheetFunction.MMult(WorksheetFunction.MInverse(C), D)
            F1 = F(1, 1)
            F2 = F(2, 1)
            K4 = dz1 * F1
            L4 = dz1 * F2
            Z3 = Z1 + dz1 / 2
            Del4 = Del1 + K3
            W4 = W1 + L3
            C(1, 1) = Del4 * W4
            C(1, 2) = Del4 ^ 2
            C(2, 1) = ((A2 - B2) * Del4 * W4 ^ 2)
            C(2, 2) = ((A2 - 2 * B2 + 1) * Del4 ^ 2 * W4)
            D(1, 1) = B1 / A1
            D(2, 1) = C2 * W4
            
            Del1 = Del1 + (K1 + 2 * K2 + 2 * K3 + K4) / 6
            W1 = W1 + (L1 + 2 * L2 + 2 * L3 + L4) / 6
            Del1St(IZ) = Del1  'Type Mismatch
            W1St(IZ) = W1     'Type Mismatch
            Z1St(IZ) = Z1       'Type Mismatch
'       Adjust Z1
            Z1 = Z1 + dz1
        Next IZ

' Spin Chamber
'    Coefficients
        A3 = A1
        B3 = A2
        B33 = B2
        C3 = B1
        B4 = C2
        A4 = A1
        ActiveSheet.Range("R10") = A3
        ActiveSheet.Range("R11") = B3
        ActiveSheet.Range("R12") = B33
        ActiveSheet.Range("R13") = C3
        ActiveSheet.Range("R14") = B4
        ActiveSheet.Range("R15") = A4

' Spray Orifice
        Omega = ActiveSheet.Range("H25")
        Re = ActiveSheet.Range("H26")
        R = Ror
    
' Solve Momentum Equations
      
        
End Sub