The cool thing with angles, is that the angle corresponds to the length of the side it's facing. With this, we know that angle B causes a side length of 9; just as well, it is 45 degrees. It also just so happens that angle A is 45 degrees as well. This means that side Y is 9 units long as well.
Now for side X!
We can use the Pythagorean Theorem for this:
X^2=9^2*9^2
X^2=81+81
X^2=162
Now we square root to find:
X=12.73
I hope this Helps!
