On the day that his first child was born, Ezio Auditore de Firenze deposited $6,200 into an investment account. The only purpose for the account was to pay for his son's first year of college tuition. Assume that his son, Flavia, started college on his 18th birthday and his first year tuition payment had to be made that day. The amount needed on that day was $45,000. If that was indeed the amount of money in the account on Flavia's 18th birthday, what annual rate of return did Ezio earn on his investment account?