To find the value of x in the given scenario, we need to apply the properties of parallel lines and angles.

**1. Understanding Parallel Lines**

Parallel lines are lines that are always the same distance apart and never intersect. When two or more lines are parallel, they have the same slope. In this case, we are given that line AB is parallel to line CD.

**2. Corresponding Angles**

When a transversal (a line that intersects two or more lines) intersects parallel lines, several angle relationships are formed. One of these relationships is the correspondence between corresponding angles.

Corresponding angles are formed when the transversal intersects two parallel lines, and they are located in the same position relative to the transversal on each line. Corresponding angles are equal in measure.

In this case, angle B and angle D are corresponding angles because they are located in the same position relative to transversal CD on lines AB and CD, respectively.

**3. Finding the Value of x**

We are given that angle B is 120° and angle D is 140°. Since angle B and angle D are corresponding angles, they must be equal in measure.

Therefore, we can set up the following equation:

120° = 140° - x

To solve for x, we can subtract 140° from both sides:

-20° = -x

We can now multiply both sides by -1 to isolate x:

20° = x

Hence, the value of x is 20°.

**Conclusion**

In summary, when AB is parallel to CD, and angle B is 120° and angle D is 140°, the value of x is 20°. This is determined by the fact that angle B and angle D are corresponding angles, and corresponding angles formed by parallel lines are equal in measure.

No, it's wrong question, it can't be the question of lines and angles. Please check the chapter as well as the question. And if you found it click the picture of that question and ATTACH here.