Given an initial quantity , how much time it takes to obtain an amount, by compound interest
the time expected is t in the formula
5000 (( 1+ 7/100) ^ t = 8000
then
( 1+ 7/100) ^t = (8000/5000) = 8/5
then
( 1 + 0.07) ^ 7.013 = 1.60 = 8/5
then the right answer is 7.013 years