A cuboid swimming pool is 40 meters long, 20 meters wide, and 4 meters deep. The four walls are made of marble with an area of 4 square meters. How many pieces of marble are needed?
一个长方体游泳池，长40米，宽20米，深4米，四壁用面积是4平方米的大理石砌成，需要大理石多少块？
<gadget id="calculator">40 * 4 * 2</gadget>
<output>320</output>

<gadget id="calculator">20 * 4 * 2</gadget>
<output>160</output>

<gadget id="calculator">320 + 160</gadget>
<output>480</output>

<gadget id="calculator">480 / 4</gadget>
<output>120</output>

<result>120</result>