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

I'm literally doing this right now for homework. Use the equations y = ax^2+bx+c and - b/2a

Now plug in - 13/2 (-1) = - 13/-2 = 6.5 is the x coordinate

Plug in 6.5 for x into y = - 1x^2+13x

-1 (6.5) + 13 (6.5) = 78

Now I don't know if (6.5,78) is correct for the vertex but I tried. I'm sorry if I'm wrong