An airline ticket from Baltimore to Miami costs $425. A bus ticket is $125. Traveling by plane will take 5 hours, compared with 35 hours by bus. Thus, the plane costs $300 more but saves 30 hours of time. Rosemarie 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. ​ $20 per hour.
C. ​ $30 per hour.
D. ​ $100 per hour.