Six less than the product of four and a number x?

Which equations represents circles that have a diameter of 12 units and a center that lies on the y-axis? check all that apply

How do you solve a question like this?

Write an equation of the line that passes through the point (2, 3) and is perpendicular to the line x = -1. a) y = 1 b) y = 3 c) y = 0 eliminate d) y = -3