since these are alternate exterior angles, they equal each other. so you set x+10=4x-20 and solve. you add 20 to both sides, subtract x from the left side and end up dividing 30 by 3 which gets you 10. now this is only the first step as you know x equals 10 but the angle does not equal 10. now you know x = 10 and you can substitute it into the angles separately. so you do (10)+10 to get one angle and get 20 degrees. then you do 4(10)-20 and you get 20 degrees.
x=10
measure of angle x+10=20
measure of angle 4x-20=20
hope this helps