how to graph this circle?

If you have completed the square to get something of the form

(x-a)² + (y-b)² = r², then the radius is r and the centre is the point (a,b).

So you have

4x² + 40x + 4y² + 40y + 191 = 0.

Let's divide through by 4:

x² + 10x + y² + 10y + 47.75 = 0

We can write this as

x² + 10x + 25 + y² + 10y + 25 + 47.75 - 50 = 0, and noticing the first three terms are (x+5)² and the next three are (y+5)², and tidying up,

(x+5)² + (y+5)² = 2.25, and noting that 2.25 = 1.5²,

this is of the desired form with a = -5, b = -5, r = 1.5. So the centre of the circle is the point (-5,-5) and its radius is 1.5.