Answer:
The mean is 11.5 minutes and the standard deviation is of 6.64 minutes
Explanation:
An uniform probability is a case of probability in which each outcome is equally as likely.
For this situation, we have a lower limit of the distribution that we call a and an upper limit that we call b.
The mean is:

The standard deviation is:

Arrival time of 9:18 am and a late arrival time of 9:41 am.
9:41 is 23 minutes from 9:18. So the time is uniformily distributed between 0 and 23 minutes, so a = 0, b = 23.
Mean:

Standard deviation:

The mean is 11.5 minutes and the standard deviation is of 6.64 minutes