A square and a rectangle have the same perimeter. The length of the rectangle is 15 cm and the width is 9 cm. What is the side length of the square in cm?
一个正方形和一个长方形的周长相等，长方形的长是15厘米，宽是9厘米，则正方形的边长是多少厘米．
<gadget id="calculator">15 + 9</gadget>
<output>24</output>

<gadget id="calculator">24 * 2</gadget>
<output>48</output>

<gadget id="calculator">48 / 4</gadget>
<output>12</output>

<result>12</result>