Okay so you can find the angle by working out the angle in the top right corner of the backwards 'Z' shape. Because there's 180 degrees in a straight line, that top right angle is 180 - 132 = 48.
Now we know that the top right angle is 48, so the angle you're looking for is 48, because they're alternate angles.
That means 3x + 9 = 48. You can find x by rearranging.
3x + 9 = 48
3x = 48 - 9
3x = 39
x = 13.
x is equal to 13.