A trapezoidal vegetable field has an upper base of 7 meters, a lower base of 5.5 meters, and a height of 5 meters. This year, 400 kilograms of vegetables are harvested, so how many kilograms of vegetables are harvested per square meter?
一块梯形菜地，它的上底是7米，下底是5.5米，高5米．今年收菜400千克，那么每平方米收菜多少千克？
<gadget id="calculator">5.5 + 7</gadget>
<output>12.5</output>

<gadget id="calculator">5 / 2</gadget>
<output>5/2 = around 2.5</output>

<gadget id="calculator">12.5 * (5/2)</gadget>
<output>31.25</output>

<gadget id="calculator">400 / 31.25</gadget>
<output>12.8</output>

<result>12.8</result>