Guess and Check type of question

Question

Uncle Wesley spent $84 at a book store. He bought science fiction and mystery novels. The science fiction novels cost $6 apiece and the mystery novels cost $5 apiece. If Uncle Wesley bought 16 novels, how many of each type did he buy?

Answer 1

S + M = 16

6S +5M = 84

5S +5M =5(16) =80

S = 84-80 = 4 science fiction novels

M = 16-4 = 12 mystery novels

4($6) + 12($5) = 24+60 = $84