An hour of an truck driver's time is valued at $30. This is the wage Bob could make as an engineer if he did not drive during that hour. If he drives the truck, he spends $15/hour on gasoline. He would also contributes $7 per hour in insurance to residents due to emissions and $7/hour in insurance to the company.

What is the private marginal cost per hour spent driving

What is the external marginal cost per hour