Hello
i need help with a function

i have 3 columns
A is a date like jan 2012, feb 2012, ... and so on
B is an expense 10,00$, 20,00$, .... and so on
C is a category like Fuel, House, DIY, Car Repair, ... and so on

i need a function that sums all the expenses on a certain category in a year



Thanks for your help!!!!!!!!!