This is the formula to solve for the vertex.
Example Question:
Find the vertex of y = -0.5x^2 + 100x
-b/2a = -100/2(-0.5) = -100/-1 = 100
The x coordinate of the vertex is 100.
Best of Luck!
P.S. this is 1000th question i've answered :)
Probabilty = 12×(1/12)^3=1/144