The width of a rectangular box is 5 in. The height is one-third of the length x. The volume is 1815 in3.

You will need to use this formula:
Years = {log(total) -log(Principal)} ÷ log(1 + rate)
Years = [log(15,000) - log(2,500)] / log (1.0525)

4.1760912591 - 3.3979400087 / 0.0222221045 =
0.7781512504 / 0.0222221045 =

35.0169917705 years
About 35 years

You'll find the formula here: http://www.1728.org/compint2.htm
And a compound interest calculator here: http://www.1728.org/compint.htm
(You'll find both are helpful for this problem).