How Do You Find the Y-Coordinate of a Parabola's Vertex?

[csands]

Homework Statement

Sorry for such an elementary question, but I'm struggling thru Int Alg. Today's nightmare involves a downward parabola. An arch supporting a bridge has the equation y=-0.0022x^2 + 1.578x + 0. Position of left side parabolic arch is (0,0). Using x = -b/2a, I calculated the symmetrical point of the parabola at (358.6363,0). If this is correct, the vertex x-coordinate is 179.31815. I'm stuck at finding the y coordinate of the vertex. Any help would be greatly appreciated.

Homework Equations

The Attempt at a Solution

 

[kuruman]

You know that y=-0.0022x^2 + 1.578x. What is y when x = 179.31815?