I know that the answer is B. I can find the total profit, but I am not sure how to get 4.2% per year

9) Rashard bought four bonds with face values of $1,000 each, a simple interest rate of 5.6% per year, and a maturity date 10 years after they were issued. He paid $4,825 three years after the bonds were issued. If he keeps the bonds until maturity, find his total profit, and his percent return per year A) $1,415; 2.9% per year C) $6,240; 18.5% per year B) $1,415; 4.2% per year D) $6,240; 12.9% per year