Can some please help me

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

We just started the introduction into circles and i have no idea how to do this.

Find the zeros of each function. f(x) = x^2 + 5x - 6