A trapezoidal vegetable field has an upper base of 20 meters, a lower base of 30 meters, and a height of 28 meters. A total of 4,200 kilograms of cabbage is harvested. How many kilograms of cabbage are harvested per square meter on average?
一块梯形菜地上底是20米，下底是30米，高是28米，共收白菜4200千克，平均每平方米收白菜多少千克？
<gadget id="calculator">20 + 30</gadget>
<output>50</output>

<gadget id="calculator">28 / 2</gadget>
<output>14</output>

<gadget id="calculator">50 * 14</gadget>
<output>700</output>

<gadget id="calculator">4_200 / 700</gadget>
<output>6</output>

<result>6</result>