We bought a total of 90 books at the store. Math books cost $4 and history books cost $5. The total price was $397. How many math books did we buy?  Choose the correct choice from the following
A) 47
B) 53
C) 56
D) 61
E) 64

Rationale: "let m be the number of math books and let h be the number of history books . m + h = 90 . h = 90 - m . 4 m + 5 h = 397 . 4 m + 5 ( 90 - m ) = 397 . - m + 450 = 397 . m = 450 - 397 = 53 . the answer is b ."
Answer: B