trapezoidal vegetable field has an upper bottom of 20 meters, a lower bottom of 30 meters, and a height of 28 meters. What is the area of the field in square meters?
一块梯形菜地上底是20米，下底是30米，高是28米，这块地的面积是多少平方米？
<gadget id="calculator">20 + 30</gadget>
<output>50</output>

<gadget id="calculator">28 / 2</gadget>
<output>14</output>

<gadget id="calculator">50 * 14</gadget>
<output>700</output>

<result>700</result>