Question

Find the angle which is double of its supplement.

Answer 1

Let the angle be 'y'.
So another angle be 'x'(Its supplement)
It means y = 2x 
x+y= 180
x+2x= 180
3x=180
x= 60 
and 
y= 2x = 2 * 60 = 120 

So, the angle which is double of its supplement is 120(degree).

Answer 2

the angle is 120° .it is supplement of 60°
  the equation is-
x+2x=180°
⇒3x = 180°
⇒x=180°/30
⇒x=60°
so ,double of its ,2x =2 x60° =120°