We bought a total of 90 books at the store. Math books cost $4 and history books cost $5. The total price was $396. How many math books did we buy? Pick one
A) 47  B) 54  C) 56  D) 61  E) 64

Rationale: "m + h = 90 h = 90 - m 4 m + 5 h = 396 4 m + 5 * ( 90 - m ) = 396 m = 54 the answer is b ."
Answer: B