When 2 angles form a linear pair, they form a straight line, that has a measure of 180°.
So, the sum of both angles is equal to 180°:
4x-20 +x =180
Solving for x:
4x+x-20=180
5x-20=180
5x=180+20
5x=200
x=200/5
x= 40
Now, replace the value of x in each angle:
4x-20 = 4(40)-20 = 160-20= 140°
x=40°
So:
Angle 1 = 140°
Angle 2 = 40°