Acar travels 18 miles per gallon of gas used. which equation best represents the proportional relationship between the y miles that the car has traveled and the x gallons of gasoline that it has used?

y = 18x is the required equation.

Step-by-step explanation:

The car traveled = y miles

Gasoline that car used to cover x miles = x gallons

Distance traveled by car is directly proportional to Gasoline used to travel that distance.

that is distance traveled by car  = K× Gasoline used  

Using unitary method,

Unitary method is used to find the value of a single unit.

Distance traveled by car  in one gallon of gas = 18 miles.

Distance traveled by car in x gallon of gas (y) = 18x miles.

Thus,  y = 18x is the required equation.