180-meter-long reservoir dam has a trapezoidal cross-section, with an upper base of 15 meters, a lower base of 5 meters, and a height of 21 meters. What is the volume of the dam in cubic meters?
一个180米长的水库大坝，横截面是梯形，上底15米，下底5米，高21米．这个大坝的体积是多少立方米．
<gadget id="calculator">15 + 5</gadget>
<output>20</output>

<gadget id="calculator">21 / 2</gadget>
<output>21/2 = around 10.5</output>

<gadget id="calculator">20 * (21/2) * 180</gadget>
<output>37_800</output>

<result>37_800</result>