Suppose you own a river that many people want to cross by car. You've recently bought a fleet of ferry boats, and you've been charging people to take their cars across the river. It's just occurred to you that if you built a toll bridge, the trip would be faster and people would be willing to pay more per crossing.
Unfortunately, if you build the toll bridge, the ferry boats must all be scrapped; they have no alternative uses. Which of the following numbers are relevant to the decision of whether to build the bridge:
a. The cost of building the bridge.
b. The revenue you could earn from a bridge.
c. The cost of the ferry boats.
d. The revenue you earn from the ferry boats.