The parabola opens upward and is symmetric to the y-axis.
Its general form is: . y \;=\;ax^2 + c
Its y-intercept is (0, 10) . . . Hence: . y \;=\;ax^2 + 10
It passes through (200, 100).
We have: . 100 \:=\:a\cdot200^2 + 10 \quad\Rightarrow\quad a \:=\:\frac{9}{4000}
Hence: . y \;=\;\tfrac{9}{4000}x^2 + 10
When x = \pm50,\;\;y \:=\:\tfrac{9}{4000}(50^2) + 10 \:=\:\frac{125}{8}
Therefore, 50 feet from the center, the cable is 15\tfrac{5}{8} feet high.
