A triangle has 180 degrees. A straight angle has 180 degrees.
The straight line is 6x. Also, a triangle has 180. So, x=30.
(I don't know your level, so I don't know how to explain it. I don't think you have learned too much about triangles yet, so I'm super sorry if you don't get my explanation.)
[180 - 4x] + [180 - 2x] + x =180, solve for x
x = 36, 2x =2 x 36 =72, 4x =4 x 36 =144