The correct answer is: 15 minutes.
A motor trolley is a type of vehicle that is used to transport people and goods around a building or campus. It is typically powered by an electric motor and has a small platform that can be used to carry passengers or cargo.
When a motor trolley is in charge of an office, it is responsible for transporting employees to and from their workstations. The trolley will typically wait at the outermost facing points of the building for 15 minutes before returning to the office. This allows employees to have enough time to get to their workstations and start working.
The other options are incorrect because they are not the amount of time that a motor trolley waits at the outermost facing points of a building. Option A is 10 minutes, option B is 20 minutes, and option D is 25 minutes.