The given equation y = 3x^2+9x is in the form y = ax^2+bx+c
Since a = 3 and b = 9, this means,
h = -b/(2a)
h = -9/(2*3)
h = -9/6
h = -3/2
h = -1.5
is the x coordinate of the vertex (h,k)
As a fraction, the answer is -3/2
In decimal form, that answer is -1.5
(use long division or a calculator to find that -3/2 = -1.5)
