You can easily imagine a circle around your graphic. And then you remember that a circle has a total of 360 degrees all the way around the center.
This means that the following sum 4x + 2x + 3x = 360
⇔ 9x = 360
We divide both side by 9 and we get :
⇔ x = 360 / 9 = 40
So X value is 40°.