The graph below shows the position of a car (in miles from Gackle, ND) as a function of time (in minutes).

Estimate the instantaneous rate of change of the car's position at the moment $t = 80$. Include units in your answer.
Instantaneous rate of change = .

Here is a list of units that WeBWorK understands.

Write a sentence to explain your reasoning and the meaning of this value.

In order to get credit for this problem all answers must be correct.