The shape of a vegetable field is a right-angled trapezoid, and the lower base is 20 meters. After increasing the upper base by 10 meters, it becomes a square vegetable field. How many square meters does this trapezoidal vegetable field occupy?
一块菜地的形状是直角梯形，下底是20米，把上底增加10米后就成了一个正方形菜地，这个梯形菜地占地多少平方米？
<gadget id="calculator">20 - 10</gadget>
<output>10</output>

<gadget id="calculator">10 + 20</gadget>
<output>30</output>

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

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

<result>300</result>