Angle x is supplementary to the angle with 156 degrees. What this means is that the sum of the two angles is 180 degrees. With this knowledge you can make a formula like so...
156 + x = 180
Now you can solve for x by subtracting 156 to both sides
156 - 156 + x = 180 - 156
x = 24
Hope this helped!
~Just a girl in love with Shawn Mendes