1. **State the problem:** Find the surface area of a rectangular prism with dimensions length $l=5$ km, width $w=3$ km, and height $h=4$ km. 2. **Formula:** The surface area $SA$ of a rectangular prism is given by: $$SA = 2(lw + lh + wh)$$ This formula adds the areas of all six faces: two each of length-width, length-height, and width-height. 3. **Calculate each area:** - $lw = 5 \times 3 = 15$ - $lh = 5 \times 4 = 20$ - $wh = 3 \times 4 = 12$ 4. **Sum the areas:** $$lw + lh + wh = 15 + 20 + 12 = 47$$ 5. **Multiply by 2:** $$SA = 2 \times 47 = 94$$ 6. **Final answer:** The surface area of the rectangular prism is $\boxed{94}$ km$^2$.