1. **State the problem:** We need to find the depth of the water in a rectangular cuboid container given the volume of water in milliliters (ml). Since 1 ml = 1 cm³, the volume of water in ml equals the volume in cubic centimeters. 2. **Given dimensions:** The container has width $w = 5$ cm, depth $d = 4$ cm, and height $h = 10$ cm. 3. **Formula for volume of a cuboid:** $$V = \text{width} \times \text{depth} \times \text{height}$$ 4. **Important rule:** The volume of water is the product of the base area (width × depth) and the water height (depth of water). If $x$ is the water depth, then $$V = w \times d \times x$$ 5. **Find water depth:** Rearranging the formula to solve for $x$: $$x = \frac{V}{w \times d}$$ 6. **Example:** If the volume of water is given (say $V$ ml), substitute the values: $$x = \frac{V}{5 \times 4} = \frac{V}{20}$$ 7. **Interpretation:** The water depth $x$ in cm is the volume of water divided by 20. **Final answer:** $$\boxed{x = \frac{V}{20} \text{ cm}}$$ This means for every 20 ml of water, the water level rises by 1 cm in the container.