Solve for the unknown number of years in each of the following (Enter rounded answers as directed, but do not use rounded numbers in intermediate calculations. Round your answers to 2 decimal places (e.g., 32.16)):

Present Value Years Interest Rate Future Value
$ 800 10 % $ 1,655
2,491 8 4,250
33,905 13 392,620
33,600 20 214,844