Respuesta :

charstar
if you add it all together it will be 180 so to work it out you would do this...
7x+40=180
7x=140
x=20

hope this helps :)
EliseJoyMyers
a supplementary angle means two angles that equal 180°

 4x + 40 + 3x = 180

7x + 40 = 180
       -40     -40
     ----------------
7x = 140       140 ÷ 7 = 20