Questions on the pic

Aline on the wall and a line on the floor are skew. always, sometimes, or never?

On a architect's drawing of a house, 1 inche representa 1.5

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