Choice B is correct. Since Peter’s car is traveling at an average speed of 50 miles per hour and the car’s gas mileage is 21 miles per gallon, the number of gallons of gas used each hour can be found by (50/1) * (1/21) = 50 /21.

The car uses 50 /21 gallons of gas per hour, so it uses (50 /21)t gallons of gas in t hours. The car’s gas tank has 17 gallons of gas at the beginning of the trip. Therefore, the function that models the number of gallons of gas remaining in the tank t hours after the trip begins is f(t) = 17 - (50t/21)