The correct answer is 40 million additional visitors per year.
Suppose the first bill is passed, raising the probability of catching any given terrorist from 10% to 20%. However, this isn't enough for some. One representative introduces a bill that would increase security by an additional 10 percentage points, from 20% to 30%. Again, assume these measures do not change the position of the blue curve.
The opportunity cost of this additional measure is 40 million additional visitors per year.
