A vegetable field is trapezoidal, with an upper base of 350 meters, a lower base of 650 meters, and a height of 70 meters. How many hectares does this land cover?
一块菜地是梯形，上底是350米，下底是650米，高是70米，这块地合多少公顷？
<gadget id="calculator">350 + 650</gadget>
<output>1_000</output>

<gadget id="calculator">70 / 2 / 10_000</gadget>
<output>7/2_000 = around 0.0035</output>

<gadget id="calculator">1_000 * (7/2_000)</gadget>
<output>7/2 = around 3.5</output>

<result>7/2 = around 3.5</result>