If your investment doubles in 6 3/4 years, what approximate annual rate of return would you have earned? If you could earn an annual rate of 7.50%, approximately how long would it take for your investment to double?

A. 9.60%; 10.67 years

B. 13.50%; 9.20 years

C. 9.20%; 13.50 years

D. 10.67%; 9.60 years

answer is NOT 10.81 and 9.58 !