Simple solution to system of three equations I've been given the question;

$$xy = \frac19$$
  $$x(y+1) = \frac79$$
  $$y(x+1) = \frac5{18}$$
  What is the value of $(x+1)(y+1)$?

Of course, you could solve for $x$ and $y$, then substitute in the values. However, my teacher says there is a quick solution that only requires $2$ lines to solve.
How can I solve $(x+1)(y+1)$ without finding $x$ and $y$, given the values above?

Multiply the second by third then substitute the first.
