I am trying to find a way of using a formula for a large range of data that
would do a sum if formula or equivalent. Below is an example of what I am
looking of knowns are what is in columns a, b and c. D is where the formula
is. It needs to give the totals of what is in c if a and b match.

A b c d
1 10 1 10 20
2 10 1 10 20
3 10 2 12 12
4 15 1 12 23
5 15 1 11 23
6 16 5 12 12
7 17 2 12 12