The skating rink was originally 50 meters long and 40 meters wide. After the expansion, the length increased by 30 meters and the width increased by 20 meters. How many square meters has the area increased after the expansion?
溜冰场原来长50米，宽40米，扩建后长增加了30米，宽增加了20米．扩建后面积增加了多少平方米？
<gadget id="calculator">50 + 30</gadget>
<output>80</output>

<gadget id="calculator">40 + 20</gadget>
<output>60</output>

<gadget id="calculator">80 * 60</gadget>
<output>4_800</output>

<gadget id="calculator">50 * 40</gadget>
<output>2_000</output>

<gadget id="calculator">4_800 - 2_000</gadget>
<output>2_800</output>

<result>2_800</result>