If the lines m and n are parallel, the angles made when passing through the same line are identical.
In this case, we know the obtuse angle has a measurement of 108 which is identical to the angle next to x, and the total angle of a line is 180. With this, we can find the angle opposite of this by subtracting 108 from 180 (180 - 108) giving us 72 degrees.
I hope this helps. Let me know if you need anything else explained