Can someone explain C & D ?

6. Problem 28-15 (Effective Rate of Interest) eBook Effective Rate of Interest Find the interest rate (or rates of return) in each of the following situations. Do not round intermediate calculations. Round your answers to the nearest whole number a. You borrow $650 and promise to pay back $689 at the end of 1 year. 6 % b. You lend $650 and receive a promise to be paid $689 at the end of 1 year 6 % c. You borrow $65,000 and promise to pay back $224,398 at the end of 13 years. % d. You borrow $16,000 and promise to make payments of $5,001.00 at the end of each of the next 5 years. %