A greeting card is 20cm long and 10cm wide, with a gold border around it. What is the length of the gold border?
一张贺卡长20cm，宽10cm，在它的四周镶上金边线，金边线的长度是多少？
<gadget id="calculator">20 + 10</gadget>
<output>30</output>

<gadget id="calculator">30 * 2</gadget>
<output>60</output>

<result>60</result>