1. **Stating the problem:** We have triangle ABC with sides $AB=4$ cm, $BC=6$ cm, and $AC=3.5$ cm. Points $E$ and $F$ are midpoints of sides $AB$ and $AC$ respectively. We need to find the length of segment $EF$. 2. **Formula used:** The segment joining the midpoints of two sides of a triangle is parallel to the third side and its length is half the length of that third side. This is called the Midsegment Theorem. 3. **Applying the theorem:** Since $E$ and $F$ are midpoints of $AB$ and $AC$, segment $EF$ is parallel to $BC$ and $$EF = \frac{1}{2} BC$$ 4. **Calculate $EF$:** $$EF = \frac{1}{2} \times 6 = 3 \text{ cm}$$ 5. **Conclusion:** The length of segment $EF$ is 3 cm. This is a direct application of the Midsegment Theorem in geometry.