Hello, This is my first post so please be nice

Find the radius & co-ordinates of the centre of the circle for the following

x^2 + y^2 - 4x - 6y = 0

x^2 + y^2 - 11x + 8y -12 = 0

3x^2 + 3y^2 - 12x - 15y + 30 = 0

Please could someone link me to a guide of how to work them out or even go through the process of how to do it for me

Any Help is very must appreciated

Thanks