VBA Sum Dynamic Range

Thanks Leith! This definitely solved it. One more related question regarding the code below. For i below, how would I replace the value 10 to instead find the
last non blank value in column D and keep filling i till the end?Thanks

Sub FindFirstNonEmptyCell()
Dim i, j, k As Integer 'i = row number, j = collumn number
    For i = 3 To 10 'replace '1 and 2' to the desires range
        For j = 5 To 256 'or 16384 in Excel2007
            If Not IsEmpty(Cells(i, j)) Then
                Cells(i, j).Copy Sheets(2).Cells(i, 1) 'the first value will be copied to sheet 2
                Exit For
            End If
        Next
    Next
    
End Sub