So this problem is asking for the difference in the total amount of gas in the tank and the amount of gas consumed. You have the total amount of gas–15 gallons. You have the information in the problem to find the amount of gas consumed.
The car can go 32 miles before consuming a full gallon of gas and it traveled 384 miles. So if you divide the 384 miles by 32 miles per gallon, you are left with the gallons consumed.
Once you have this number, you can subtract it from 15 gallons–the total amount of gas in the tank–to get how much gas is left.