Find the directrix, focus , and roots of the parabola y= x^2 - 5x + 4....... ok here is where I am so far

First thing i did was isolate the x variables so i can complete the square.

y - 4= x^2 - 5x

Then i completed the square...

y-4 = x^2 - 5x half of - 5= -5/2 and squaring that i got 25/4 so i added that to both sides....

y-4 + 25/4 = x^2 -5x + 25/4

simplified....

y+9/4 = ( x- 5/2) ^2

and now i dont know how to get my "a" to complete my parabola equation y-k = a(x-h)^2 .....i can solve the problem if i knew how to get it... please help!