piece of iron wire forms a rectangle with a length of 20 cm and a width of 10 cm. If this wire is used to form a square, what is the side length?
一根铁丝围成一个长20厘米，宽10厘米的长方形，如果用这根铁丝围成一个正方形，边长是多少？
<gadget id="calculator">20 + 10</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>