Searching for 2 values and returning the sum...

I quite often have this problem, and I have never come up with a solution...

In this example I have customers coming to our restaurant at Christmas. We
have food orders for each customer. I want to be able to look for all the
customers sat on table 1 (in one column) and count how many people want (for
example) soup (in another column). Any obvious functions I am missing?