Answer
The same for a linear function regardless of the interval chosen.
Work Step by Step
The units of the average rate of change of $f$ are units of $f(x)$ per (additional) unit of $x$.
The average rate of change in deaths of manatees per additional boat is the same for a linear function regardless of the interval chosen. This is because a line has constant slope $m$ which equals the average rate of change between any two points.
