Analytics Software

Hi folks,

i am new bee to obiee, i need to calculate last 3,6,9,12 months avg from the prompted month

Please note that i am not doing any ago calculations in rpd,i want to do it in answers only.. i have a rev.date prompt,with the selected date how can i find the 3,6,9,12 months avg in single report.

like

sales amount(SELECTED MONTH) product 3 months avg sales,6 months avg,9M avg

2000 1 200 150 100

i tried with Filter function in column formula but couldn't make it ---Filter(sales amount using rev.date ='@{pv_month}{Mar-12}')--here how can i add last 3 months?
Please through some light on this?

Thanks in advance
ganga