Answer:
The unit rate is 20.8 ft/ sec.
Step-by-step explanation:
It is given that the displacement of 644.8 ft in 31 s.
When the rate is define in the quantity of 1, then it is called unit rate.
In 31 s the displacement is 644.8 ft.

Divide both sides by 31,


For one second the value of the displacement is 20.8.
Therefore the unit rate for 644.8 ft in 31 s is 20.8 ft/sec.