1. **State the problem:** We need to find the area of the dotted blue triangle inside a rectangle with width 6 cm and height 4 cm. 2. **Formula for the area of a triangle:** The area $A$ of a triangle is given by $$A = \frac{1}{2} \times \text{base} \times \text{height}$$ 3. **Identify base and height:** The dotted blue triangle is right-angled and formed by the diagonal of the rectangle. The base can be taken as 6 cm (width of the rectangle) and the height as 4 cm (height of the rectangle). 4. **Calculate the area:** $$A = \frac{1}{2} \times 6 \times 4 = \frac{1}{2} \times 24 = 12$$ 5. **Conclusion:** The area of the dotted blue triangle is 12 square centimeters.