Average Speed
Jack swims nine lengths of a 25 meter long swimming pool in 2 minutes and 32.1 seconds.
So, total distance
and time

Thus, average speed of Jack

Now, Jill swims ten lengths of the 25 meter long swimming pool in the same time interval.
So, the total distance
and time

Thus, average speed of Jill

Average Velocity
As Jack swims nine lengths of the pool, it means he ends up at the opposite end of the pool from where he started. So, the net displacement = 25 meter
Thus, average velocity of Jack

Now, Jill swims ten length of the pool, it means he ends up at the starting position. So, the net displacement = 0 meter
Thus, average velocity of Jill
meter/second.