Suppose an airline ticket from Charlotte to Dallas 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