1. **Problem statement:** Given a rectangular prism with volume $V = 200$ cm³, width $w = 4$ cm, height $h = 10$ cm, find the length $l$. 2. **Formula used:** The volume of a rectangular prism is given by $$V = l \times w \times h$$ where $l$ is length, $w$ is width, and $h$ is height. 3. **Rearranging the formula to find length:** $$l = \frac{V}{w \times h}$$ 4. **Substitute the known values:** $$l = \frac{200}{4 \times 10}$$ 5. **Calculate the denominator:** $$4 \times 10 = 40$$ 6. **Calculate the length:** $$l = \frac{200}{40} = 5$$ 7. **Answer:** The length $l$ is 5 cm. This means the rectangular prism has dimensions length = 5 cm, width = 4 cm, and height = 10 cm to have a volume of 200 cm³.