Do you know how to solve this problem?

The vertex can be found at x=0, i.e, h=290. The vertex tells us that the bridge is 290 ft. high at its' midpoint. The max width is when y=0, or, in other words:
0.0159x²=290
x²=290/.0159= 18239
x=±135.05
The distance between the feet of the arch is 2x135.05, or 270.10
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1+1=22×1=22-1=11-1=1duh