To make a packing box for a microwave oven, the length is 7m, the width is 5m, and the height is 4m. At least how many square meters of cardboard should be used?
做一个微波炉的包装箱，长7m，宽5m，高4m，至少要用多少平方米的硬纸板？
<gadget id="calculator">7 * 5</gadget>
<output>35</output>

<gadget id="calculator">7 * 4</gadget>
<output>28</output>

<gadget id="calculator">5 * 4</gadget>
<output>20</output>

<gadget id="calculator">35 + 28 + 20</gadget>
<output>83</output>

<gadget id="calculator">83 * 2</gadget>
<output>166</output>

<result>166</result>