I don’t know what I’m doing wrong. But my answer comes up to 896. What am I doing wrong?
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As has been pointed out, the four choices are all wrong.
The first, 48,960, is the VOLUME of the large box.
The second, 38,880, is the VOLUME of the small box if its HEIGHT, rather than length, is 7 cm less.
The third, 10,080, is the difference of those, so it would be correct for a modified form of the problem.
The fourth, 5,440, is something I can't find.
The picture looks clearly like an open-top box. You correctly found the surface areas of both boxes including the top. (I can follow your work, but you didn't make it easy!)
The problem is HORRIBLE in several ways -- it doesn't tell you whether to count the top, doesn't tell you which dimension is which (though I think your choice is reasonable), and has very wrong choices. It even describes a "shipping box" but shows a "storage box"! And it says "small" where it means "large" ("small ... the same as the small, but ...")! I wonder if they showed the wrong picture.