There is a square vegetable field with a circumference of 40 meters. If every square meter of vegetable land can receive 3 kilograms of green vegetables. How many kilograms of vegetables are harvested in this vegetable field?
有一块正方形菜地，周长40米．如果每平方米菜地可收青菜3千克．这块菜地共收青菜多少千克？
<gadget id="calculator">40 / 4</gadget>
<output>10</output>

<gadget id="calculator">10 * 10 * 3</gadget>
<output>300</output>

<result>300</result>