Assuming that by "16t2" you mean
:
First of all, let's compute the position at the two required times:


So, the ball traveled a total distance of
, during the time
.
The average rate of change is the ratio between these two:

Answer:
-2x
Step-by-step explanation:
Let the width be w, then length = 2w - 1
Area = length times width = w(2w - 1) = 21.
Thus, 2w^2 - w = 21 or 2w^2 - w - 21 = 0
Solving the quadratic equation gives that w = 3.5.
Therefore, width is 3.5 ft and length is 2(3.5) - 1 = 6 ft.