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

雖然看過參考帖,但還是不理解,請幫忙, 謝謝

2. f(v)=2^x3^y5^z

f(m)=2^x3^y+25^z

^v=100x+10y+z

^{m=100x+10(y+2)+z}

^m-v=20