I've been reading and searching all over to no avail.

Is it possible to do another calcation on the subtotal line for the
column that was excluded in the subtotal?

If instance,

ColA ColB ColC ColD
A 1 10 ""
A 2 20 ""
B 2 20 ""
B 3 20 ""

Sum ColB, ColC nothing for ColD
Result
A 3 30 ""
B 5 40 ""

But I want do to a calcuation after I get the subtotal to get the
following
Desired Result (Where ColD is a calcuation of ColB-ColA for the
Subtotal row)
A 3 30 27
B 4 40 35


TIA