Well the knowledge of it I just simply forgot about and don't remember a single thing about how to do it.

Write the equation of a circle with center (4,0) and passing through the point (12,6).

I don't want just an answer, I need the method of how to do it. Also I might also need help understanding this question as well

Write the equation of a circle with center (6,6) and tangent in both axes.

THANKS!!!