Answer: x = 40
Step-by-step explanation:
Always when you have a line and another line that cuts it, two consecutive angles always add up to 180° (the plane angle)
Then, in this case we can see that:
x + (4*x - 20) = 180
for the internal angle of the right and the external one.
now, we can solve this equation for x.
x + 4*x - 20 = 180
5*x = 180 + 20 = 200
x = 200/5 = 40
