1. **Problem Statement:** We have two vertical parallel walls, one 4 meters high and the other 6 meters high. A man stands upright between them, and we want to find the height of the man. 2. **Understanding the Setup:** The tops and bottoms of the walls are connected by lines crossing above the man. This forms two similar triangles because the walls and the lines create proportional segments. 3. **Key Concept - Similar Triangles:** When two triangles are similar, their corresponding sides are proportional. Here, the height of the man corresponds to a segment between the crossing lines. 4. **Using the Intercept Theorem (Thales' Theorem):** The height of the man $h$ can be found by the formula: $$h = \frac{4 \times 6}{4 + 6}$$ This formula comes from the property that the height divides the segment proportionally between the two walls. 5. **Calculate the Height:** $$h = \frac{24}{10} = 2.4$$ So, the height of the man is 2.4 meters. 6. **Alternative Explanation:** Imagine the man standing exactly where the two crossing lines meet. The height is like the harmonic mean of the two wall heights because the man’s height balances the proportions between the walls. 7. **Summary:** The man’s height is 2.4 meters, found by using similar triangles and the intercept theorem between the two walls.