1. **Problem Statement:** Given a triangle with a segment parallel to the top side inside it, the top side is 10, the left side is split into 4 and 12, and the inner parallel segment is labeled ?. Find the missing length. 2. **Formula and Concept:** When a segment is drawn parallel to one side of a triangle, it creates similar triangles. The corresponding sides of similar triangles are proportional. The proportion is: $$\frac{\text{segment 1}}{\text{segment 2}} = \frac{\text{parallel segment 1}}{\text{parallel segment 2}}$$ 3. **Set up the proportion:** Here, the segments on the left side are 4 and 12, and the top side is split into 10 and ?. So, $$\frac{4}{12} = \frac{?}{10}$$ 4. **Solve for ?:** $$\frac{4}{12} = \frac{?}{10} \implies ? = \frac{4}{12} \times 10$$ 5. **Simplify the fraction:** $$? = \frac{\cancel{4}}{\cancel{12}} \times 10 = \frac{1}{3} \times 10$$ 6. **Calculate the value:** $$? = \frac{10}{3} = 3.33$$ **Final answer:** The missing length is approximately $3.33$.