11. Master Wang drives from location A to location B to deliver goods. If he travels at a speed of 60 kilometers per hour both ways, he can return to location A on time. However, upon arriving at location B, he finds that his speed from A to B was only 55 kilometers per hour. If he wants to return to location A on time, at what speed should he drive back?
66 kilometers/hour
11.【Solution】Master Wang should travel every 2 kilometers in $\frac{1}{60} \times 2$ (hours). Now, he travels every 1 kilometer at $\frac{1}{55}$ hours,
so he should travel every 1 kilometer on the return trip: $\frac{1}{60} \times 2 - \frac{1}{55} = \frac{1}{66}$ (hours).
That is, he should drive back at a speed of 66 kilometers per hour.

【Another Solution】According to the problem, if Master Wang travels at a speed of 60 kilometers per hour for both the outbound and return trips,
he will return to point A on time. This means that the planned time to travel 1 kilometer is $\frac{1}{60}$ hours. However, Master Wang's actual speed from point A to point B is only 55 kilometers per hour, so the actual time to travel 1 kilometer is $\frac{1}{55}$ hours, which is $\left(\frac{1}{55} - \frac{1}{60}\right)$ hours more than planned. To return to point A on time, Master Wang must spend $\left(\frac{1}{55} - \frac{1}{60}\right)$ hours less than planned for each kilometer on the return trip. That is, he can only spend $\frac{1}{60} - \left(\frac{1}{55} - \frac{1}{60}\right) = \frac{1}{66}$ (hours) per kilometer. Therefore, Master Wang should drive back at a speed of 66 kilometers per hour.

Answer: Master Wang should drive back at a speed of 66 kilometers per hour.