## Precalculus (6th Edition) Blitzer

$90\ ft$
Step 1. Using the given figure, set the middle of bridge as the origin. We can write the general form of the equation for the parabola as $x^2=4py$ Step 2. As the point $(400,160)$ is on the curve, we have $400^2=4p(160)$, which gives $p=250$ Step 3. At 100 feet from the right tower, we have $x=400-100=300$. Thus $y=\frac{x^2}{4p}=\frac{300^2}{4(250)}=90\ ft$