If "P" means "-", "Q" means "/", "R" means "+", and "S" means "*" then find the value of the following:

21 Q 7 R 9 S 10 P 13

80

21 Q 7 R 9 S 10 P 13
= 21 / 7 + 9 * 10 - 13
= 3 + 90 - 13
= 80

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