the expected returns for each of the projects are as follows: buying a new delivery van, 20%; computer training for its office staff, 15%; and defensive driving training for its drivers, 8%. if the current interest rate is 10%, the firm should invest in a. only the office staff training project. b. all of the projects because the average of the returns is greater than 10%. c. only the purchase of a new delivery van. d. the purchase of a new delivery van and computer training for its office staff.