We have to calculate profits for each number of workers:
1 worker: total revenue : $42; profit: 42 - 11 = $31
2 workers: t. r. ($10 + $14) = $ 24 * 3 = $72; profit: 72 - 22 = $50
3 workers: t. r. $90, profit: 90 - 33 = $57
4 workers: t. r. $105; profit : 105 - 44 = $61
5 workers: t. r. $117; profit: 117 - 55 = $62
6 workers: t. r. $126, profit: 126 - 66 = $60
7 workers: t. r. $132, profit: 132 - 77 = $55
Answer: Manfred will hire 5 workers to maximize the profit.