How to calculate Sales percentage difference between selected year and its previous year in a Matrix

Hi,

I'm trying to generate a report using matrix like this

                                                      Month

Product     PreviousYearSalesAmount    SelectedYearSalesAmount      %SalesDifference

I can populate year sales amount, but i cant calculate the percentage.

Can Anyone help me please.

Note: Month and Year are passed as parameters.

Thank you.