Joe invested a certain sum of money in a simple interest bond whose value grew to $560 at the end of 3 years and to $660 at the end of another 5 years. What was the rate of interest in which he invested his sum?
Options:
A) 3 %
B) 4 %
C) 5 %
D) 6 %
E) 7 %

Rationale: "in 5 years , the value grew $ 100 , so the simple interest was $ 20 per year . in 3 years , the total interest was 3 * $ 20 = $ 60 the principal is $ 560 - $ 60 = 500 . the interest rate is $ 20 / $ 500 = 4 % the answer is b ."
Answer: B