Setting aggregation level to Average

Hi All,There is a member in ACCOUNT dimension - "WT Avg Contract Monthly Fee"

There is a MARKET dimension which has MARKET(parent)->"WT Total Region"->"WT Total->"WT West","WT East","WT North","WT South"I need to bring in a cross section of data in a form wherein I need to display Average value of "WT Avg Contract Monthly Fee" at the "WT Total" level instead of sum.How to set the aggregation method as Average ?

In simple terms, if the value of "WT Avg Contract Monthly Fee" is 4 for each of the regions "WT West","WT East","WT North","WT South" at the "WT Total" level it should show 4 instead of 16.