Final answer:
The total change in the gallons of gas in Garrett's car tank after driving 7.8 miles to his grandma's house is -0.468 gallons.
Step-by-step explanation:
The question involves calculating the total change in the gallons of gas in a car tank given the change in gas per mile driven. Garrett drives 7.8 miles to his grandma’s house and for every mile he drives, the amount of gas in the car tank changes by -0.06 gallons. To find the total change, we multiply the number of miles driven by the change in gas per mile.
Total change in gallons of gas = (Number of miles driven) × (Change in gas per mile)
Total change in gallons of gas = 7.8 miles × -0.06 gallons/mile
Total change in gallons of gas = -0.468 gallons
This means that after driving to his grandma's house, Garrett will have used up 0.468 gallons of gas.