A.) it's a 90° angle
90=6x+4x+10
90=10x+10
-10 -10
80=10x
divide both sides by 10, x=8
B.) it's a 180° angle
180=5x+13+3x+7
180=8x+20
-20 -20
160=8x
divide both sides by 8, x=20
C.) it's a 180° angle
180=3x+5+2x+18+2x+17
180=7x+40
-40 -40
140=7x
divide both sides by 7, x=20
D.) it's a 180° angle
180=90+30+x
180=120+x
-120 -120
60=x
