Answer: -2.4 gallons per hour
Explanation:
Think of this as a linear equation where the rate of change is m.
m = (Y₂ - Y₁) / (X₂ - X₁)
Assume the points are: (2, 15) (7, 3)
m = (3 - 15) / (7 - 2)
= (-12) / 5
= - 2.4 gallons per hour
Gas is reducing by 2.4 gallons per hour.