Question

A tunnel is in the shape of a parabola. The maximum height is 31 m and it is 13 m wide at the base as shown below.

Answer 1

First start out with the y=a(x-h)+k we know it's upside down, so a is negative a

Answer 2

y=a(x-h)+k is certainly workable. Think carefully: (h,k) would be the VERTEX. What are the appropriate values for h and k? I'd strongly suggest that you draw this upside-down parabola.