we know that
Supplementary angles are those angles whose sum is equal to [tex] 180[/tex] degrees
In this problem
[tex] x+y=180[/tex] --------> equation [tex] 1 [/tex]
[tex] x=3y [/tex] --------> equation [tex] 2 [/tex]
Substitute the equation [tex] 2 [/tex] in equation [tex] 1 [/tex]
[tex] [3y]+y=180 [/tex]
[tex] 4y=180 [/tex]
[tex] y=45[/tex]°
Find the value of x
[tex] x=3*45 [/tex]
[tex] x=135[/tex]°
therefore
the answer is
The measure of angle x is [tex] 135[/tex]°
