Answer:
6.47 gal
Step-by-step explanation:
cost of gas per gallon = $2.78
rate of change is cost of gas per gallon as cost to buy gas changes with the change in quantity of gallon.
Total cost for x gallons = cost of gas per gallon*x = 2.78x
Given that total money paid by him is $18
2.78x = 18
x = 18/2.78 = 6.47
