Which number has two lines of symmetry?

Pls! does anybody know a shortcut for answering these types of questions in the future?

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

Add the fractions, and simply the result to lowest terms. 2/3 + 2/7= ?