An hour of a truck driver is valued at $20, which is the wage that Bob would make as a security officer if he did not drive during that hour. If he drives the truck, he would be spending $15 on gas. He would also then need to contribute $7 per hour in insurance for the city and another $6 in insurance for the truck company.

What is the private marginal cost of Bob?

What is the external marginal cost?

Both in per hours