try this: it might give you an idea on what you want to achieve

[vba]
'Cdbl convert the string for computation

Sub try()

Dim totalprice As Double

Numone = InputBox("Please enter the price of the car")
Numtwo = InputBox("Please enter the delivery fee")
NumThree = InputBox("Please enter the trade in amount")
totalprice = CDbl(Numone) + CDbl(Numtwo) - CDbl(NumThree)
MsgBox totalprice

End Sub[/vba]

ohhh..this one is for your class project..you must try to learn and understand what you are doing. so that one day.. you will learn to stand and not to lean on.. cheers study hard..