The main cable of a suspension bridge forms a parabola, described by the equation
y = a(x - 1)2 + k, where y is the height in feet of
the cable above the roadway, x is the horizontal
distance in feet from the left bridge support, a is a
constant, and (h, k) is the vertex of the parabola.
At a horizontal distance of 30 ft, the cable is 15 ft
above the roadway. The lowest point of the cable
is 6ft above the roadway and is a horizontal
distance of 90 ft from the left bridge support.