A saver has been depositing money in a fixed-interest bank account for the last 10 years. If the balance of his account is $15,432 at time t = 10, calculate an approximate value of the annual interest rate earned. You are given that the investor deposited $2000 at time t = 0, $3000 at time t = 3.5, and $5600 at t = 7. You should perform a simple “pen-and-paper” calculation.