1. **State the problem:** We need to find the area of a right triangle with one leg measuring 60 mm and the other leg measuring 21 cm. 2. **Convert units to be consistent:** - 60 mm = 6 cm (since 10 mm = 1 cm) - The other leg is already 21 cm 3. **Recall the formula for the area of a right triangle:** $$\text{Area} = \frac{1}{2} \times \text{base} \times \text{height}$$ 4. **Substitute the values:** $$\text{Area} = \frac{1}{2} \times 6 \times 21$$ 5. **Calculate the area:** $$\text{Area} = \frac{1}{2} \times 126 = 63$$ 6. **Final answer:** The area of the triangle is $63$ square centimeters.