I hope this helps you find the answer you're looking for
12, 24, 36, 48, 60,
15, 30, 45, 60
The 60th caller will win both.
Approximately 15.4 years
I multiplied 20,000 by 0.13 and got 2,600. Then I subtracted 20,000 from 60,000 to get 40,000. Finally I did 40,000 / 2,600 and got 15.4