A rectangular vegetable field is 20 meters long and 10 meters wide. After expansion, the length increases by 10 meters and the width increases by 5 meters. How many square meters does the area increase?
一块长方形菜地长20米、宽10米，扩建后，长增加10米，宽增加5米，面积增加多少平方米？
<gadget id="calculator">20 + 10</gadget>
<output>30</output>

<gadget id="calculator">10 + 5</gadget>
<output>15</output>

<gadget id="calculator">30 * 15</gadget>
<output>450</output>

<gadget id="calculator">20 * 10</gadget>
<output>200</output>

<gadget id="calculator">450 - 200</gadget>
<output>250</output>

<result>250</result>