Calculating ED and CST combined

Hi Friends,

I'm trying to combine ED (Excise duty) and CST for Purchase process.

ED is calculated at 12.5% based on assessable value and added to the

Total amount and CST 2% calculated on the resulting value.

E.g  GRPO amount - Rs 44045 (based on unit price * qty)

       Assessable value - Rs 30544 | ED 12.5% is calculated on this - Rs 3818

       Total = 44045 + 3818 = 47863

       CST 2% on 47863 = 957.26

       Grand Total = 47863 + 957.26 = 48820.26

From above its obvious both ED and CST should be combined into one tax code.

I need help in coding the Tax formula to arrive at the required amount. Please help.

With Thanks & Regards

Shiva Venkat