Answer: 1 unit of lenght per second (it may be meters, but there is no enough information)
Explanation:
If t is time and s is position, we have that:
in t= 0s, s(t) = 0
in t= 8s, s(t) = 8
Then, we can see that the swimmer moved 8 units in the lapse of 8 seconds, and the average speed can be calculated as:
s = distance/time = 8units/8s = 1 unit per second.
So the average speed of the swimmer in that lapse of time is one unit per second, where unit depend on the problem, here may be metters.
