(1 pt) A traffic expert wants to estimate the maximum number of cars that can safely travel on a particular road at a given speed.

(1 pt) A traffic expert wants to estimate the maximum number of cars that can safely travel on a particular road at a given speed. He assumes that each car is 15 feet long, travels at speed , and follows the car in front of it at a safe distance for that speed. He finds that the number of cars that can pass a given spot per minute is modeled by the function 81x/16+16(x/21)^2