The diagram shows two parallel lines and a transversal intersecting them. One of the angles formed is 140°, and the other angle (denoted as $x^\circ$) is on the opposite side of the transversal.

By the properties of parallel lines and a transversal, we know that the angle marked $140^\circ$ and $x^\circ$ are supplementary because they are on the same side of the transversal. This means they add up to $180^\circ$.

Thus, we can find $x$ using the equation:

$x + 140^\circ = 180^\circ$

Solving for $x$:

$x = 180^\circ - 140^\circ = 40^\circ$

So, the value of $x$ is 40°.

Would you like further clarification or details on this? Here are 5 related questions:

1. What are alternate interior angles, and how do they relate to parallel lines?
2. How can you identify corresponding angles in parallel line diagrams?
3. Can you explain the concept of supplementary angles more generally?
4. How does the transversal affect the angles when it intersects two parallel lines?
5. What are some common mistakes students make when identifying angle relationships in diagrams?

Tip: When dealing with angles in parallel lines, always check whether the angles are supplementary, corresponding, or alternate to determine their relationships quickly.