To find the rate of change in the number of gallons in the pool after each hour has passed, we can use the formula:
Rate of change = (y2 - y1) / (x2 - x1)
Plugging in the values:
Rate of change = (80 - 160) / (3 - 1) = -80 / 2 = -40
Therefore, the rate of change in the number of gallons in the pool after each hour has passed is -40 gallons/hour.
The correct answer is: -40 gal./hr.