请教一道涛涛数学题，谢谢大家了！

Q2:

The function f is defined for each positive three-digit integer n by f(n) = 2^x3^y5^z, where x, y and z are the hundreds, tens, and units digits of n, respectively.  If m and v are three-digit positive integers such that f(m) = 9f(v), then m-v = ?

A.   8

B.   9

C.   18

D.   20

E.   80

Answer: D

20啊

因为9=3的平方，也就是说f(m)在3的指数比f(v)高2

换句话说，m的十位数比v的十位数大2，其他的都一样，那么相减的话就是20