Calculations Translation- Bex vs Transformation

Hello gurus,

here is the line that I d like to translate in BW, and I d like to know what's the better way of implementing it in BW, is it in Transformation (formula/calculation), or in Bex.

result = (1/3) x (sum of prior 3 month balance from date entered) x (number of days in the past 3 months) / (sum of prior 3 month sales)

Assumption is that user 's input is 1 Month period. (please write the line in abap if you re thinking that it is easier).

Thanks,