About finding equivalent resistance
One way to solve it would be to connect a 1 volt source between X and Y, then use nodal analysis to determine the source current. There are six nodes (not counting X and Y), so six equations would be needed. The equivalent resistance is the voltage divided by the current.

Another way is to take advantage of symmetry, as in your previous question. Remove \$R_{PQ}\$ and \$R_{RS}\$. Now look at nodes P, Q, R, and S. Each one is halfway between X and Y in terms of resistance along their branch. This means that they all should have the same voltage, which is \$\frac {V_X - V_Y} 2\$. Since they have the same voltage, a resistor connected between any two of the points won't draw any current. Thus, \$R_{PQ}\$ and \$R_{RS}\$ can be ignored. Now the circuit is a straightforward series and parallel resistor problem.