Got partial credit on this- dont know what is incorrect

A coin sold at auction in 2017 for $4,573,500. The coin had a face value of $2 when it was issued in 1789 and had previously been sold for $285,000 in 1968. At what annual rate did the coin appreciate from its first minting to the 1968 sale? (Do not round intermediate calculations and enter your answer as a percent rounded to 2 decimal places,e.g., 32.16.) What annual rate did the 1968 buyer earn on his purchase? (Do not round intermediate calculations and enter your answer as a percent rounded to 2 decimal places, e.g., 32.16.) At what annual rate did the coin appreciate from its first minting to the 2017 sale? (Do not round intermediate calculations and enter your answer as a percent rounded to 2 decimal places, e.g., 32.16.) a. b. c. a. Rate of return from 1789 to 1968 b. Rate of return from 1968 to 2017 c. Rate of return from 1789 to 2017 6.85 % 6.22 % 6.72 %