A trapezoidal lawn has an upper base of 250 meters, a lower base of 150 meters, and a height of 180 meters. What is its area in hectares?
一块梯形的草地，上底250米，下底150米，高是180米，它的面积是多少公顷？
<gadget id="calculator">250 + 150</gadget>
<output>400</output>

<gadget id="calculator">180 / 2 / 10_000</gadget>
<output>9/1_000 = around 0.009</output>

<gadget id="calculator">400 * (9/1_000)</gadget>
<output>18/5 = around 3.6</output>

<result>18/5 = around 3.6</result>