Answer:
I = 1575 / 5000 = 31.5 % interest on investment
(1 + i)^18 = 1.315 where i interest is earned per year
One can use logs or
1 + i = 1.315^1/18 = 1.0153
So the annual interest rate is .0153 or 1.53%
Or
5000 (1 + i)^18 = 6575
(1 + i)^18 = 1.315
18 log (1 + i) = log 1.315
log (1 + i) = .006607
1 + i = 1.0153
i = .0153 = 1.53%
