A rectangular piece of land is 15 meters long and 4 meters wide. A total of 420 kilograms of rapeseed was harvested in this field. How many kilograms were harvested on average per square meter?
一块长方形地，长15米，宽4米．在这块地里一共收油菜420千克，平均每平方米收多少千克？
<gadget id="calculator">15 * 4</gadget>
<output>60</output>

<gadget id="calculator">420 / 60</gadget>
<output>7</output>

<result>7</result>