Answer:
x = 20
Step-by-step explanation:
The three angles make up a straight line.
A straight line has 180 degrees.
x + 3x + 100 = x80 Combine
4x + 100 = 180 Subtract 100 from both sides
4x = 180 - 100
4x = 80 Divide by 4
x = 80/4
