You can put this solution on YOUR website! Set y=0 to find the points where the graph crosses the x-axis:
-5x^2 + 25x + 70 = 0
We can simplify by dividing through by -5:
x^2 - 5x - 14 = 0
x = (5 +- sqrt(25 + 56))/2 -> (5 +- 9)/2, or x = -2,7
The vertex lies on the line of symmetry half way between these 2 points:
x = (-2+7)/2, or x = 5/2
To get the y-coordinate, substitute into original equation:
-5*(5/2)^2 + 25(5/2) + 70 = -125/4 + 125/2 + 70 = 125/4 + 280/4 = 101 1/4
Ans: vertex = (2 1/2,101 1/4)
