Formula to collect average of Amount per G/L Account

Hello Experts,

I just started working on BPC and have been given a scenario to work on.

I will be loading data from BW to BPC and I would like to collect the AMOUNT value from BW into BPC as the average of all amounts per G/L Account.

G/L Account     Amount

ACC001               120

ACC001               130

ACC002               150

ACC002               160

ACC002               180

ACC003               200

ACC003               200

I would like the output in BPC to be -

ACC001               125

ACC002               245

ACC003               200

Kindly guide me in this scenario.