Hello there! The fornula for compound interest is P(1 + r/n)^nt. P = principal, r = interest rate, n = number of times compounded, and t = time in years. Let's do this. The interest rate is 7%, and it is compounded quarterly, which is four times per year. Let's divide 7% (0.07) by 4. 0.07/4 is 0.0175. Let's add that number to 1. 1 + 0.0175 is 1.0175. Before we do something to this number, we multiply the amount of times compounded per year by the number of years. In this case, we will multiply 4 by 4, because the time period is 4 years. 4 * 4 is 16. Now going back to the other number, we will raise 1.0175 by the 16th power. 1.0175^16 power is 1.319929351. There is a long decimal on the calculator, but do not delete this from your calculator. Multiply that number by the principal, which is 5,000. When you do, you get 6,599.646756 or 6,599.65 when rounded to the nearest cent. There. Thomas's account will have $6,599.65 after 4 years.