The task is to generate the correct answer for a given math problem.

Problem: 20 is subtracted from 80 % of a number , the result is 60 . find the number ?
100

Problem: a can do a work in 15 days and b in 20 days . if they work on it together for 7 days , then the fraction of the work that is left is
11 / 6

Problem: if w / x = 2 / 3 and w / y = 6 / 15 , then ( x + y ) / y =

8 / 5