A piece of iron wire forms a rectangle with a length of 18 cm and a width of 12 cm. If it is used to enclose a square, what is the side length in cm?
一根铁丝围成一个长18厘米，宽12厘米的长方形，如果用它重围一个正方形，边长是多少厘米？
<gadget id="calculator">12 + 18</gadget>
<output>30</output>

<gadget id="calculator">2 / 4</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">30 * (1/2)</gadget>
<output>15</output>

<result>15</result>