if your car can travel 75 miles for every 3 gallons of gas, you need to find how much miles it travels on 1 mile. to do this, do 75/3 = 25. so, your car can travel 25 miles per gallon. now multiply by 7 since you have 7 gallons of gas. 25•7= 175. in short, your car will travel 175 miles with 7 gallons of gas left.