A square vegetable field with a side length of 20 meters can harvest 2 kilograms of tomatoes per square meter. How many kilograms of tomatoes can be harvested in this field?
一块正方形菜地，边长为20米，每平方米能收获西红柿2千克，这块地一共能收获西红柿多少千克？
<gadget id="calculator">20 * 20</gadget>
<output>400</output>

<gadget id="calculator">400 * 2</gadget>
<output>800</output>

<result>800</result>