This a vertical parabola but upside down so x term is squared.
The general equation of a parabola is y=a+k
Where, (h,k)= vertex of the parabola
The parabola has vertex at origin, so (h,k) =(0,0)
So, the equation becomes, y=a
Now, the width is 16 meters, So the x-intercepts must be x=-8 and x=+8
So, the points are (-8,-16) and (+8,-16)
To find the value of 'a' Let us plug x=-8, y=-16 in y=a
So, We get, -16=a
-16=a*64
Dividing by 64 on both sides
a=
a=-0.25
So, the equation of parabola becomes
y=-0.25
We need to find vertical clearance 7m from the edge of the tunnel.
As, edge is at x=8, 7m from the edge is x=8-7=1
So, we need to find vertical clearance, or y, 7m , from the edge of the tunnel, or x=1
Now plugging x=1 in y=-0.25
y=-0.25
y=-0.25*1
y=-0.25
Vertical clearance= height-y value=16-0.25=15.75
So, Answer=15.75meters