Can't figure this out

Question

A footbridge is in the shape of an arc of a circle. The bridge is 4.2 ft tall and 18 ft wide. What is the radius of

the circle that contains the bridge? Round to the nearest tenth.

Answer 1

Use the intersecting chord theorem.

Draw and label a diagram - sketch in the circle.

x represents the distance from the bridge to the "bottom" of the circle.

4.2x = (9)(9)

4.2x = 81

x ≈ 19.2857

The diameter is 4.2 + 19.2857

 

So what is the radius?