An experimental model for a suspension bridge is built in the shape of a parabolic arch. In one section, cable runs from the top of one tower down to the roadway, just touching it there, and up again to the top of a second tower. The towers are both 9 inches tall and stand 60 inches apart. Find the vertical distance from the roadway to the cable at a point on the road 12 inches from the lowest point of the cable.