The equation for a support span is given by h = − 1/40(x − 20)^2, where h metres is the distance below the base of a bridge and x metres is the distance from the left side.

Question

a) What is the turning point of the graph?
b) What is the width of the support span?

Answer 1

Your equation represents a parabola with vertex (20,0), that would be the turning point.
So the vertex of (20,0) would be half-way between the endpoints of the width
so when x = 0, h = -(1/40)(400) = -10
when x = 40 , h = -10
(the -10 suggests 10 m below)

So the width is 40 m.

I don't like the wording of this question.

Answer 2

Ahah, thanks so much for your help!