Answer
See below.
Work Step by Step
The general equation for a circle with radius $r$ and centre $(h,k)$ is: $(x-h)^2+(y-k)^2=r^2$, hence our equation:
$x^2-2x+y^2+4x=4\\(x^2-2x+1)-1+(y^2+4x+4)-4=4\\(x-1)^2+(y+2)^2=9=3^2$
Thus the center is at $(1,-2)$ and the radius is $3$.
