How to calculate 30 days back data in webi

Hello gurus,

I have come across a requirement where user wants to see only 30 days data in the chart.

We have user prompts for Begin and End date. The begin date is always constant (01-01-yyyy) but end date keeps changing.

So, suppose user enters End date as Feb 28 then chart should show data for 28 days of feb and two days of Jan.

How can I do that any suggestions...I researched on google and found some threads but none of them seems to be resolving my issue.

Any suggestions?

Regards

Shirley