packing charges on excise

Hi gurus ,

I've a requirement - excise , cst to be calculated on packing & forwarding charges too .

In our , existing system of excise is calculating like this manner -

1. Basic Value

B. P&F 2% = A*2% ,

C. Excise Duty 12.5% , = A*12.5% ,

D. CST 2% = (A +C)*2%

Total = (A+B+C+D) .

But , as of requirement - need to be configured like this way ;

A. Basic Value
B. P&F 2% = A*2%
C. Excise Duty 12.5% = (A+B)*12.5%
D. CST 2% = (A+B+C)*2%

Total = (A+B+C+D) .

What's necessary steps to be required for its implementing ? attaching existing, m/08 screen shot.

Regards

Patel