B3. A bus passes by three stops. The middle stop is as far from the first stop as it is from the last stop. Fred is standing at the middle stop and has to wait 15 minutes for the bus to arrive. If he bikes to the first stop, he will arrive there at the same time as the bus. If he runs to the last stop instead, he will also arrive there at the same time as the bus.

How long would it take Fred to bike to the last stop and then run back to the middle stop?
B3. 30 minutes The time Fred takes to cycle from the middle stop to the last stop and then run back to the middle stop is equal to the time it takes him to cycle from the middle stop to the first stop plus the time he needs to run from the middle stop to the last stop. After all, the distances to the two stops are equal.

Given that this is exactly equal to the time the bus needs to drive to the first stop plus the time to drive to the last stop. This together is exactly equal to twice the time the bus needs to drive to the middle stop: $2 \times 15=30$ minutes.