To find the rate of change (slope) between the two points (1,160) and (3,80), we can use the formula for the slope between two points \((x_1, y_1)\) and \((x_2, y_2)\):
\[ \text{slope} = \frac{y_2 - y_1}{x_2 - x_1} \]
Here, we have:
- \( (x_1, y_1) = (1, 160) \)
- \( (x_2, y_2) = (3, 80) \)
Substituting these values into the slope formula gives:
\[ \text{slope} = \frac{80 - 160}{3 - 1} = \frac{-80}{2} = -40 \]
Thus, the rate of change in the number of gallons in the pool is \(-40 , \text{gal./hr.}\)
The correct response is therefore: −40 gal./hr.