The equation that models this situation is m = 18g
Solution:
Given that,
Amount of average of miles on each gallon of gas = 18 miles
Let the number of miles be "m"
Let "g" be the number of gallons of gas
According to question,
Number of miles= Average of miles on each gallon of gas x Number of gallons of gas

m = 18g
Thus the equation that models this situation is m = 18g