Answer
See below.
Work Step by Step
$x^2+y^2-10x+4y+20=0\\(x-5)^2-25+(y+2)^2-4+20=0\\(x-5)^2+(y+2)^2=9=3^2$
The general equation for a circle with radius $r$ and centre $(h,k)$ is: $(x-h)^2+(y-k)^2=r^2$, hence here the center is $(5,-2)$ and the radius is $3.$
