Parabola word problem

Question

 the towers of a parabolic suspension bridge Are 100 meters apart and each tower stands 40 m above the road. At its closest point, the main cable which forms the parabola is 5 m above the road. How high would a worker walking on the main cable be when he’s 20 feet from the left tower?

Answer 1

y = a x² + b; (x = ±50 m, y = 40 m); (x = 0 m, y = 5 m); solve for a & b; then calculate y at x = (50 m – 20 ft)