Solve for the unknown number of years in each of the following:

1) present value = 610, interest rate = 10%, future value = $1,747

2) present value = 860, interest rate = 11%, future value = $2,200

3) present value = 18,900, interest rate = 16%, future value = $275,672

4) present value = 22,000, interest rate = 13%, future value = $321,293