Need help (example file uploaded): Search Account# and Sum Balance

Hello helpful people,

I need creating a formula that will allow me to search an account # and have it sum the balances of said account. This is what the data looks like: Screen Shot 2013-05-21 at 1.05.23 PM.png

I'm using Excel 2008 for Mac - I'd like the user of the excel file to be able to enter an account number - say 51x Bouska L and have the formula return a value that sums a total balance.

Thanks!

Use a SUMIF.
=SUMIF(range, criteria, sum_range)
range: your first column
criteria: value that the user enters
sum_range: second column