Can someone please help me with the following problem as a whole day of
surfing over the internet did not help:

I want to make a selection that when column A is cost and column B is apple
that the answer is 80 (sum of column C) as in the spreadsheet below:
A B C
cost apple 10
cost tomato 20
revenue apple 50
revenue tomato 30
cost apple 30
revenue tomato 20
cost tomato 10
cost apple 40

Your help is much appreciated!

Best regards,

Frank