Insert a formula in a cell via VBA using reference cells

[mblake5]

I know there are various threads out there about this, but I haven't been able to make this work. I am trying to input a formula (and it needs to be a formula, not just the current answer) that is

activecell.offset(2,0).formula = sum(activecell:selection.end(x1up))*activecell.offset(2,-2)

I know this formula doesn't work, but I cannot seem to figure out what the correct syntax is. As an example, my cursor is in J6 and I need the sum of J6:J? (the last continuous cell with data above J6), multiplied by H8, and put the formula in J8.

And I cannot used the fixed cell numbers on any of it, because I never know how large the table is that I'm manipulating.

 

[mikerickson]

With Range(ActiveCell, Selection.End(xlup))
    ActiveCell.Offset(2, 0).FormulaR1C1 = "=SUM(" & .Address(True, True, xlR1C1) & ")+RC[-2]"
End With