To find the rate of change in the number of gallons in the wading pool, we can use the formula for the slope between two points on a graph, which is given by:
\[ \text{slope} = \frac{y_2 - y_1}{x_2 - x_1} \]
Given the points (1, 160) and (3, 80):
- \( (x_1, y_1) = (1, 160) \)
- \( (x_2, y_2) = (3, 80) \)
Substituting the values into the formula:
\[ \text{slope} = \frac{80 - 160}{3 - 1} = \frac{-80}{2} = -40 \]
The rate of change in the number of gallons in the pool after each hour has passed is \(-40\) gallons per hour.
Thus, the correct response is:
−40 gal./hr.