The cables for the central span of a suspension bridge take the shape of a parabola. If

Question:

The cables for the central span of a suspension bridge take the shape of a parabola. If the towers are 800 meters apart and the cables are attached to them at points 400 meters above the floor of the bridge, how long must the vertical strut be that is 100 meters from the tower? Assume that the cable touches the bridge deck at the midpoint of the bridge Figure 10.