A stunt motorcyclist makes a jump from one ramp 20 feet off the ground to another ramp 20 feet off the ground. The jump between the ramps can be modeled by LaTeX: y\:=\:-\frac{1}{640}x^2+\frac{1}{4} x\:+\:20y = − 1 640 x 2 + 1 4 x + 20 where x is the horizontal distance (in feet) and y is the height above the ground (in feet). What is the distance between the ramps?