1. **State the problem:** Find the volume of a rectangular prism with dimensions given by the number of unit cubes along its length, width, and height. 2. **Formula:** The volume $V$ of a rectangular prism is calculated by multiplying its length $l$, width $w$, and height $h$: $$V = l \times w \times h$$ 3. **Given dimensions:** - Length $l = 5$ cubes - Height $h = 3$ cubes - Depth (width) $w = 8$ cubes 4. **Calculate the volume:** $$V = 5 \times 3 \times 8$$ 5. **Multiply step-by-step:** $$5 \times 3 = 15$$ $$15 \times 8 = 120$$ 6. **Final answer:** The volume of the rectangular prism is **120 cubic units**.