Excel 2007 : getting the average purchase figure for the 4 largest stocks

Hi,
My data set is a financial dataset and i need this to be done.

My spreadsheet looks like this

volume--------------------------------------returns
(s1) (s2) (s3) (s4) -------------------(s1) (s2) (s3) (s4)

1 2 3 4 ------------------------------5 6 4 2

s1......4 are 4 different stocks and returns and volume data are given seperately. i want to get the average of the volume of the 2 stocks that have highest returns, in the above case, I want to average volume of s1 and s2 as they have the highest returns. Please help me. Thank you