I want to perform the same two calculations on some sheets in my workbook which contain tables of different row length

I'm trying to perform two calculations on a table to work out averages. Then do the same calculations in each sheet in my workbook. There are 'x' number of sheets. The tables in each sheet are dynamic in length. There's errors in this code that I'm trying to resolve

sub AvgCalculations

'x is a dynamic value and is the number of sheets in a workbook
For n = 3 to x

'Calculation 1   This calculates Average profit per unit
Sheets(n).range("B" & lastRow).Offset(2, 0).Value = Sheets(n).range("P" & lastRow).Offset(2).Value / 
Sheets(n).range("I" & lastRow).Offset(2).Value


'Calculation 2    This calculates Average profit per order
'Sheets(n).range("A" & lastRow).Offset(2, 0).Value = Sheets(n).range("P" & lastRow).Offset(2).Value 
/row("D").Column.Count

Application.ScreenUpdating = True

Next n

End Sub