1. **State the problem:** Calculate the surface area (SA) of a rectangular prism with dimensions 5 cm (height), 4 cm (width), and 80 mm (length). 2. **Convert all dimensions to the same unit:** Since 80 mm = 8 cm, the dimensions are 5 cm, 4 cm, and 8 cm. 3. **Formula for surface area of a rectangular prism:** $$SA = 2(lw + lh + wh)$$ where $l$ = length, $w$ = width, $h$ = height. 4. **Substitute the values:** $$SA = 2(8 \times 4 + 8 \times 5 + 4 \times 5)$$ 5. **Calculate each product:** $$8 \times 4 = 32$$ $$8 \times 5 = 40$$ $$4 \times 5 = 20$$ 6. **Sum the products:** $$32 + 40 + 20 = 92$$ 7. **Calculate the surface area:** $$SA = 2 \times 92 = 184$$ 8. **Final answer:** The surface area is $184$ cm$^2$.