How do you solve this

Geometry paper. i don't know how to do the rest. questions 5. 8. 9. and 10.

The general form of the quetion of a circle is ax^2+by^2+cx+dy+e=0 where a=b=0 if the circle has a radius of three units and the center lies on the y axis which set of values of a, b, c, d, and e might correspond to the circle

The radius of the earth is two times the radius of the moon. what fraction of the volume of the earth is the volume of the moon?