Thanks
y = 4x2 - 28x - 17
y + 17 = 4x2 - 28x (add 17 to both sides)
y + 17 = 4(x2 - 7x) (factor)
y + 17 + 49 = 4(x2 - 7x + 49/4) (complete the square)
y + 66 = 4(x - 7/2)2 (factor)
Now, select the vertex from the equation.