Final answer:
The mean change in water level per hour is 2.6 m/h.
Step-by-step explanation:
The mean change in water level per hour can be calculated by dividing the total change in water level (14.3 m) by the time taken (5.5 h). Therefore, the mean change in water level per hour is:
Mean change in water level per hour = (Total change in water level) / (Time taken) = 14.3 m / 5.5 h = 2.6 m/h
Therefore, the correct answer is (a) 2.6 m/h.