Solved: VBA function procedure homework help

[gaross]

[VBA][/VBA]I need help with an assignment I've been working on. I feel like I'm completely lost on this. It's driving me crazy.

The assignment states:

"Create a VBA function procedure called R_K to evaluate the Redlich-Kwong equation of state given in problem 11 on page 327 (attached jpg). Note that there is confusion in the text between v (lowercase) and V (uppercase). All instances should be v, with units of L/mole. Do not use the values of T and v given in the problem statement; those should be a function arguments so the user can choose values. Remember that a function procedure must be stored in a standard module in order to be executed from the Excel worksheet."

The instructor is a little off his rocker and over half the class has dropped so far (9 weeks in). Any help would be greatly appreciated!!

This is my code plus I have a chart for the data in excel:

[VBA]Option Explicit
Type CompoundData
compound As String
ctemp As Double
cpres As Double
End Type
Sub temp_press_data()
Dim RK(4) As CompoundData
RK(1).compound = "Methane"
RK(1).ctemp = 190.6
RK(1).cpres = 45.4
RK(2).compound = "Ethylene"
RK(2).ctemp = 282.4
RK(2).cpres = 49.7
RK(3).compound = "Nitrogen"
RK(3).ctemp = 126.2
RK(3).cpres = 33.5
RK(4).compound = "Water (vapor)"
RK(4).ctemp = 647.1
RK(4).cpres = 217.6
Call R_K
End Sub
Public Function R_K()
Dim R As Double, T As Double, P As Double, V As Double, a As Double, b As Double, x As Integer
Dim RK(4) As CompoundData
x = InputBox("Please select a compound from the chart")
T = InputBox("Please enter temperature (K)")
V = InputBox("Please enter volume (L)")
R = 0.08205
If x = 1 Then
a = 0.427 * (((R ^ (2)) * (RK(1).ctemp ^ (2.5)) / (RK(1).cpres)))
b = 0.0866 * R * ((RK(1).ctemp) / (RK(1).cpres))
P = ((R * T) / (V - b)) - ((a) / (V * (V + b) * Sqr(T)))
ElseIf x = 2 Then
a = 0.427 * (((R ^ (2)) * (RK(2).ctemp ^ (2.5)) / (RK(2).cpres)))
b = 0.0866 * R * ((RK(2).ctemp) / (RK(2).cpres))
P = ((R * T) / (V - b)) - ((a) / (V * (V + b) * Sqr(T)))
ElseIf x = 3 Then
a = 0.427 * (((R ^ (2)) * (RK(3).ctemp ^ (2.5)) / (RK(3).cpres)))
b = 0.0866 * R * ((RK(3).ctemp) / (RK(3).cpres))
P = ((R * T) / (V - b)) - ((a) / (V * (V + b) * Sqr(T)))
Else
a = 0.427 * (((R ^ (2)) * (RK(4).ctemp ^ (2.5)) / (RK(4).cpres)))
b = 0.0866 * R * ((RK(4).ctemp) / (RK(4).cpres))
P = ((R * T) / (V - b)) - ((a) / (V * (V + b) * Sqr(T)))
End If
End Function
[/VBA]