Abus slows down uniformly from 75.0 km/h ( 21 m/s) to 0 km/h in 21 s. how far does it travel before stopping

In this question two important things are already given . Let us first note them down first.
Speed of the bus = 75.0 km/hr or 21/s
Time before it finally stops = 21second.
It is better to calculate in miles per second as the time given is in second. This will make the problem easier.
We already know that
Distance traveled = Speed * time
                             = 21 * 21 meters
                             = 441 meters
So the bus will stop after traveling a distance of 441 meters.
This distance can be converted to kilometer as well very easily now.
1000 meter = 1 km
441 meters = 441/1000 km
                   = 0.441 km
So the bus will stop after 441 meters or 0.441 kilometers.