Since the point (25, 0) lies halfway between the x-intercepts, (15,0) and (35,0), then by the symmetry of the parabola, the point (25, 32) must be the vertex.
So, the vertex form of the equation has the form y = A(x-25)2 + 32
Since (15,0) is on the graph, we have 0 = 100A + 32
A = -32/100 = -8/25
Equation: y = (-8/25)(x-25)2 + 32

Mark M.
03/27/18