A rectangle and a square are surrounded by 50 meters of iron wire. The length of the rectangle is 8 meters and the width is 7 meters. What is the perimeter of the square?
用50米长的铁丝，围成一个长方形和一个正方形，长方形的长是8米，宽是7米，正方形的周长是多少？
<gadget id="calculator">8 + 7</gadget>
<output>15</output>

<gadget id="calculator">15 * 2</gadget>
<output>30</output>

<gadget id="calculator">50 - 30</gadget>
<output>20</output>

<result>20</result>