Solved: how to define the cells?

I am trying the following code under sheet_activate event but it gives error.
For i = 1 To 100
If Cells(12, i).Value <> "" And Cells(13, i).Value <> "" Then

Cells(14, i) = Cells(12, i).Value - 25 * Cells(13, i).Value
End If
Next

the error shows is application-defined or object-defined error. it seems the problem is with i at cells( , i) and we cannot have variable in paranteses. How to solve this problem and how to write other way?

works fine for me....I did put your operation in parenthesis so the subtraction is done before the multiplication:
[VBA]Cells(14, i) = (Cells(12, i).Value - 25) * Cells(13, i).Value[/VBA]

Do you have text in any of the cells?