3.97 A bank offers four different types of certificates of deposits (CDs) as indicated below: Total interest at maturity (%) Duration (yr) CD type 0.5 1 5 2 1.0 7 2.0 3 10 15 4 4.0 If a customer wants to invest $50,000 in various types of CDs, determine the plan that yields the maximum return at the end of the fourth year