Answer:
The annual interest rate is 41.7%.
Step-by-step explanation:
Given : If a $1,200 investment earns $210 over 5 years.
To find : What is the annual interest rate?
Solution :
Using compound interest formula,

Where, A=$1200 is the amount
P=$210 is the principal
t=5 years is the time
r is the interest rate.
Substitute the value,



Taking 5th root both side,
![\sqrt[5]{5.714}=(1+r)](https://tex.z-dn.net/?f=%5Csqrt%5B5%5D%7B5.714%7D%3D%281%2Br%29)



Interest rate in percentage, 
The annual interest rate is 41.7%.