Total surface area of a cuboid = 2(lb + bh + lh). Here lb=268, bh=36, and lh=603. So TSA = 2 × (268 + 36 + 603) = 1814 square mm. A cuboid has three pairs of equal rectangular faces: lb, bh, and lh. We add these three face areas and multiply by 2 to include the opposite faces. The answer is in square units, so the correct choice is 1814 mm².