David invested $220 in a savings account that offers a 3% return on the investment. The value of David's investment will be at least $400 after a period of ________ years.
Hint: Use the formula A = P(1 + r)t, where A is the amount after t years, P is the amount invested, r is the rate of interest, and t is the time period.
Use a calculator to compute the answer, and round it off to the nearest year.