Answer:
The answer is: B) $75
Step-by-step explanation:
Marco and Lisette should both only go once to the doctor (ophthalmologist) since the first visit will give both of them $75 in net benefit. We can calculate their net benefit by subtracting the cost of the doctor's visit from the benefit each of them gets by visiting the doctor: $150 - $75 = $75.
If any of them decided to go to the doctor twice, then they would have negative utility, since the cost of visiting the doctor would be larger than the benefit obtained form visiting him: $45 - $75 = -$30.