There is a road between the suburbs and downtown. The road becomes congested at rush hour. As long as fewer than 100 people use the road at rush hour, the trip takes 30 minutes. When the 101st person enters the road, everyone has to slow down and the trip now takes 31 minutes. People value their time at $6 per hour (i.e., $0.10 per minute) and so a 30 minute trip costs $3.

a. What is the private cost of one of the 100 individuals using the road? What is the total private cost of 100 people using the road? What is the total social cost of 100 people using the road?

b. What is the total social cost of 101 people using the road? What is the private cost of using the road for the 101st individual? What is the external social cost of the 101st person using the road?