A closed rectangular box has length 4, width 5, and height 6. If the top face of the box is removed, what is the total surface area of the…

First find the surface area of the closed box. It has three pairs of faces: $4 \times 5$, $4 \times 6$, and $5 \times 6$, so the total is $2(20 + 24 + 30) = 2(74) = 148$. Removing the top face takes away its area. The top is the face with dimensions length by width, $4 \times 5 = 20$, so the open box has $148 - 20 = 128$ square units, choice B. Choice A (148) is the closed box. Choice C (120) removes $28$ or a different face by mistake. Choice D (134) subtracts 14 instead of 20, a miscalculation with the wrong face dimensions.