I believe students are way too quick to look for formulas and equations. The hardest part of a problem usually involves understanding what we want to know and how to use what we do know to get there. Usually, we know a lot of extraneous material, and part of this step is identifying what we do know that is relevant. Moreover, to think, humans need names for things.

We want to know how many Speedy buses Travis passes. He cannot pass any Speedy Bus that arrives in Chicago before he arrives in Chicago. Nor can he pass any Speedy bus that leaves after him because he drives faster.

The only creative steps needed to solve this problem are (a) to determine the time that the last bus to arrive in Chicago before Travis's arrival left L. Geneva, and (b) relative to that time when did Travis leave L. Geneva.

We are talking relative time so, to avoid negative numbers, we can **NAME** as **ZERO** the time of departure from L. Geneva of the bus that was the last to arrive in Chicago before Travis.

Therefore that bus arrived at minute 90. Now we could mess around demonstrating it, but it is fairly obvious then that Travis arrived at minute 95.

Therefore, he left at minute (95 - 60) or 35.

Our problem reduces to: how many Speedy buses left after 0 and before 35.

You could work all day with formulas and equations to solve a fundamentally simple problem. But it becomes that simple only after thinking about what we want to know, what we know that is relevant, and naming things.

**EDIT**: As lev showed, there are frequently a number of ways to solve a problem.