do_sum in alv grid - insert some field's sum separately

I got three fields - A, B, C.

They are P type.

I use do_sum = 'X' at A, B.

But C = A / B * 100.

my question is :

I want to use do_sum at A, B.

But C is percent that I have to calculate.

Can I use do_sum and insert C field value into a sum row together?