A trapezoidal vegetable field has an upper base of 400 meters, a lower base of 650 meters, and a height of 75 meters. How many hectares does this land contain?
一块梯形菜地，上底是400米，下底是650米，高是75米，这块地合多少公顷．
<gadget id="calculator">400 + 650</gadget>
<output>1_050</output>

<gadget id="calculator">75 / 2 / 10_000</gadget>
<output>3/800 = around 0.00375</output>

<gadget id="calculator">1_050 * (3/800)</gadget>
<output>63/16 = around 3.9375</output>

<result>63/16 = around 3.9375</result>