Frank invested $10,000 8 years ago. During that time, he increased his investment by 4 times. What annual rate of return did Frank earn on this investment?

r =________________________ %

INSTRUCTIONS: Place your answer in PERCENTAGE form with at least 2 decimal places. For example, an answer of three and one-quarter percent is entered as 3.25 and not as 0.0325. ALSO, DO NOT USE A PERCENT SIGN IN YOUR ANSWER. You should work your analysis using at least four decimal places of accuracy.