To find the rate of change in the cost of gas per gallon, we can use the two points provided: \((4, 15)\) and \((8, 30)\). These points represent the number of gallons pumped (x-coordinate) and the total cost of the gas (y-coordinate).
The formula for the rate of change (slope) between two points \((x_1, y_1)\) and \((x_2, y_2)\) is given by:
\[ \text{slope} = \frac{y_2 - y_1}{x_2 - x_1} \]
Substituting the given points into the formula:
- Let \((x_1, y_1) = (4, 15)\)
- Let \((x_2, y_2) = (8, 30)\)
Now we can calculate:
\[ \text{slope} = \frac{30 - 15}{8 - 4} = \frac{15}{4} \]
Thus, the rate of change in the cost of gas as each gallon is pumped is \(\frac{15}{4}\) dollars per gallon, or \(3.75\) dollars per gallon.