Abridge on a river is modeled by the equation h = -0.2d^2 + 2.25d, where h is the height and d is the horizontal distance. for cleaning and maintenance purposes a worker wants to tie a taut rope on two ends of the bridge so that he can slide on the rope. the rope is at an angle defined by the equation -d + 6h = 21.77. if the rope is attached to the bridge at points a and b, such that point b is at a higher level than point a, at what distance from the ground level is point a?