For a trapezoidal lawn, the upper base is 30 meters, the lower base is 50 meters, and the height is 20 meters. If the lawn costs 45 yuan per square meter, how much is the total cost?
一块梯形草坪，量得它的上底是30米，下底是50米，高是20米，如果每平方米草坪需要45元，那么共需要多少元？
<gadget id="calculator">30 + 50</gadget>
<output>80</output>

<gadget id="calculator">20 / 2</gadget>
<output>10</output>

<gadget id="calculator">80 * 10</gadget>
<output>800</output>

<gadget id="calculator">45 * 800</gadget>
<output>36_000</output>

<result>36_000</result>