Physics—Highway Speed: A slightly banked highway corner will safely accommodate traffic at...

Physics—Highway Speed: A slightly banked highway corner will safely accommodate traffic at a speed given by the model

where x represents the radius of the corner in feet, and f(x) represents the speed at which the traffic can travel safely in miles per hour.

(a) Evaluate f(20) and interpret.

---

(b) If the highway planners expect the traffic to travel at a speed of 64 miles per hour, what radius should the corner be?