Final answer:
The shoe salesman would choose to work hard in this scenario because it increases the probability of a sale and therefore his earnings.
Step-by-step explanation:
The shoe salesman would choose to work hard in this scenario. Working hard increases the probability of a sale from 20% to 40%, which means he has a higher chance of earning a commission. Although working hard would cost him $20, the $40 commission per sale and $20 fixed salary would offset the cost and provide a higher overall earnings. Additionally, being under monitoring where he may get fired if he shirks reinforces the incentive to work hard.