help！有关f（x）题目！

Xiaotongdi

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
从何下手！

liuliu200507

选D吧，m和v个位和百位是一样的，因为9是三的倍数，在十位数上差2才能导致f(n)差九倍，所以2*10=20

Xiaotongdi

嗯嗯……我理解了！我弄错了，我把个位加减了！