please help this is the last question and i don’t understand

Answer: 30
Step-by-step explanation:
The angles of triangles have to add up to 180°
So:
x + x + 70 + x + 20 = 180
Bring like terms together
x + x + x + 70 + 20 = 180
3x + 90 = 180
Subtract 90 from both sides
3x = 90
Divide both sides by 3
x = 30