I need help I don’t understand

Answer:
x=50
Step-by-step explanation:
A= 30+2x
B= x
Supplementary angles are angles that always add up to 180 degrees.
therefore, A + B=180 degrees
30 + 2x + x = 180: Now we solve
30 + 3x =180
subtract 30 from both sides
3x=150
divide by 3
3x/3 = 150/3
x= 50