A square is surrounded by an iron wire. The side length of this square is exactly 20 cm. If this iron wire is used to form a rectangle with a length of 30 cm, what is the width of the rectangle?
用一根铁丝围成一个正方形，这个正方形的边长刚好是20厘米，如果用这根铁丝围成一个长30厘米的长方形，这个长方形的宽应该是多少厘米？
<gadget id="calculator">4 / 2</gadget>
<output>2</output>

<gadget id="calculator">20 * 2</gadget>
<output>40</output>

<gadget id="calculator">40 - 30</gadget>
<output>10</output>

<result>10</result>