请问Math一题

assfgrtrtr

For all real numbers V, the operation V* is defined by the equation V*=V- V/3. If (V*)*=8, then v=?

答案的解法是:

(V*)*=V*- V*/3=8(我不懂这步如何得来)

V*=12

himba

V*=V-V/3=2/3V

(v*)* = (2/3)^2 V=8

4/9 V = 8

V = 18