Given data:
The given table.
a)
The expression for average rate change of height is,

Thus, the average rate of change for the height from 0 seconds to 5.6 seconds is 25 m/s.
b)
The expression for average rate change of height is,

Thus, the average rate of change for the height from 8.4 seconds to 11.2 seconds is - 15 m/s.