Answer
The slope is 5 dollars per hour of tennis played.
Work Step by Step
To find the slope pick 2 points on the curve and find the quotient of the change in y (cost) and the change in x (hours). Using the points at 5 hours and 10 hours:
$slope=\frac{\Delta y}{\Delta x}=\frac{150-125}{10-5}=\frac{25}{5}=5$
The cost increases by \$5 for each hour of tennis played.
