An Airline Ticket from Baltimore to Miami Costs $525

An airline ticket from Baltimore to Miami costs $525. A bus ticket is $325. Traveling by plane will take 5 hours, compared with 25 hours by bus. Thus, the plane costs $200 more but saves 20 hours of time (Hint: Note how we are "thinking at the margin" here by looking at the changes) . Other things constant, an individual will gain by choosing air travel if, and only if, each hour of her time is valued at more than

A) $10 per hour.
B) $13 per hour.
C) $20 per hour.
D) $105 per hour.