How Do I Create If/Then Statements?

I have 2 columns – A and B. Column A will either be 11,12,13,14. Column B will either be 12,13,14,15. I want to have a formula in Column C that will result in a specific number (19,20,21,22,23,24) depending on the values in Column A and B.
A B. C
11. 12. 19
11. 13. 19
11. 14. 20
11. 15. 21
12. 12. 20
12. 13. 20
12. 14. 21
12. 15. 22
13. 12. 21
13. 13. 21
13. 14. 22
13. 15. 23
14. 12. 22
14. 13. 22
14. 14. 23
14. 15. 24
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Scott Levin