What is/ how do you calculate the vertex for a parabola with this equation: y=-1x^2 13x?

Y=x^2+13x
complete the square to get it into form y=a(x-h)^2+k whre (h,k) is the vertex

y=x^2+13x
y=(x^2+13x)
13/2=6.5, 6.5^2=42.25
y=(x^2+13x+42.25-42.25)
y=((x+6.5)^2-42.25)
y=(x-(-6.5))^2+(-42.25)
the vertex is (-6.5,-42.25)

The correct answer is -3.9> -4.5 gucci playa