Hi Tushar,
In this case, you can merge both the dimensions i.e. BA and PC. And in TOTAL column, you can specify formula as below:
=[Amount BI] * [Amount Excel]
Don't forget to drag only merged dimension of BA and PC in the block. By default, webi will do Full Outer join on this and multiply both the key figures. Try this and let us know if you face any issues.
Sahil