Answer:
x=20 degrees
I did what your teacher did down there; I added all the exterior angles and set them equal to 360°
Just combined the like terms and got the answer!
*3x + 4x + 3x = 10x
12 - 10 - 2 = 0
90 + 70 = 160
Put them "as an equation": 10x + 160 = 360
Get rid of what's surrounding the x, so subtract 160 from both sides.
10x = 200
To get rid of whats beside the x *again*, divided 10x by 10 on both sides.
x = 20