There is a vegetable field in the shape of a trapezoid, with an upper base of 13 meters, a lower base of 17 meters, and a height of 20 meters. Last year, a total of 6,900 kilograms of cabbage was harvested. How many kilograms of cabbage were harvested per square meter on average?
有一块菜地为梯形，上底是13米，下底17米，高是20米，去年共收白菜6900千克，平均每平方米收白菜多少千克？
<gadget id="calculator">13 + 17</gadget>
<output>30</output>

<gadget id="calculator">20 / 2</gadget>
<output>10</output>

<gadget id="calculator">30 * 10</gadget>
<output>300</output>

<gadget id="calculator">6_900 / 300</gadget>
<output>23</output>

<result>23</result>