7.3 Three work crews are to be scheduled to perform overtime work. Based on past experience under similar circumstances, the ith crew's performance on overtime is given by c;(1 ~ e'\"I") (units of work) where Ci and (1(- are constants, and If is the overtime (hours) worked by the ith crews Overtime pay to the ith crew is given by \"ifi (dollars). The total cost ofthe overtime work is to be less than or equal to $2,000. Each t, is to be selected from the set of non-negative integers. The total number of units ofwork is to be maximized a. Are the maximum-return functions concave? b. Find t]*, :5\