You deposit $2000 in an account earning 3% interest compounded monthly. How much will you have in the account in 15 years?

Use the formula
A = P * (1 + R/N)NT

Where A = the final amount
P = initial principal
R = interest rate
N = number of times interest is compounded per year
T = number of years

In this case
A = 2000 * (1 + .05/12) ^(12 * 18)

A = 2000 * (1.0041667) ^(180)
A = 2000 *(2.1137)
A = 4227.40