Question

20000=15000(1.072)^t

Answer 1

                                                 20,000 = 15,000 (1.072)^t

Divide each side by 15,000 :             4/3 = (1.072)^t

Take the log of each side:          log(4/3) = t log(1.072)

Divide each side by  log(1.072):     t = log(4/3) / log(1.072)

                                                      0.12494 / 0.03019 = 4.138  (rounded)