How to apply Excel formula in BPS layout

Hi ,

I need to apply the following logic in my BPS layout.

There are three data columns called C,D,E respectivelt

redord 1 user input data for all the columns,

Record 2 C2 = D1 + E2.

Record 3 C3 = D2 + E3.

............

Record n Cn = D(n-1) + En.

n is the number of record in teh layout.

1: Can we use Excel formula to achive this?

2: If the anser is yes, how can we configure the BPS layout? I am not sure if we can do it at the last step of change layout.

3: If the answer is no, what is the other choice? I have tried to use user exit, but had some problem in passing the data to xth_data table in the orginal order sequence.

thanks in advance.