Find the equation of a circle with radius $4$ units and touching both the co-ordinate axes having a centre in third quadrant. 

Find the centre and radius of the circle ${\mathrm{x}}^2+{\mathrm{y}}^2-2\mathrm{x} +4\mathrm{y}-4=0$

Find the centre and radius of the following 

${\mathrm{x}}^2+{\mathrm{y}}^2-6\mathrm{x}-8\mathrm{y}-24=0$

Find the centre and radius of the following

$4x^2+4y^{2 }-24x-8y-24=0$