The general form of the equation of a circle is given as
(x - h)^2 + (y - k)^2 = r^2
Hence given the circle X^2 +y^2+4x+2y-20=0
Rearranging the equation
X^2+4x+y^2+2y =20
Completing the square
X^2 +4x + 4+y^2+2y + 1= 20 + 4 + 1
factorizing
(x + 2) ^2 + (y + 1)^2 = 25
(x + 2) ^2 + (y + 1)^2 = 5^2
Comparing with the general form of the equation of a circle
(h,k) = (-2, -1)
The radius is 5