Let f(x,y) be defined as the remainder when (x–y)! is divided by x. If x=24, what is the maximum value of y for which f(x,y)=0? Choose the correct option
A) 12  B) 15  C) 18  D) 20  E) 21

Rationale: "the question is finding y such that ( 24 - y ) ! is a multiple of 24 . that means we need to have 2 ^ 3 * 3 in ( 24 - y ) ! 4 ! is the smallest factorial number with 2 ^ 3 * 3 as a factor . 24 - y = 4 y = 20 the answer is d ."
Answer: D