Answer:
0.2 = 20% probability that on a given day the previews last between 10 and 12 minutes
Explanation:
A distribution is called uniform if each outcome has the same probability of happening.
The uniform distributon has two bounds, a and b, and the probability of finding a value between c and d is given by:

It is known that the previews begin at the scheduled movie start time and they last between 5 and 15 minutes.
This means that

What is the probability that on a given day the previews last between 10 and 12 minutes?

0.2 = 20% probability that on a given day the previews last between 10 and 12 minutes