The value of x is 130°.
Solution:
The reference image for the solution is attached below.
Let A, B and C be the given angles.
m∠A = 70° and m∠C = (x – 20)°
If two lines are parallel then their corresponding angles are congruent.
Line e and line f are parallel lines and ∠B and ∠C are corresponding angles.
m∠B = m∠C
m∠B = (x – 20)°
Angle A and angle B are in the same line. So, they form a linear pair.
m∠A + m∠B = 180°
70° + x – 20° = 180°
50° + x = 180°
Subtract 50° on both sides of the equation.
x = 180° – 50°
x = 130°
The value of x is 130°.