What is the width of a rectangle with a perimeter of 60 cm and a length of 20 cm?
一个周长是60厘米的长方形，长是20厘米，宽是多少？
<gadget id="calculator">60 / 2</gadget>
<output>30</output>

<gadget id="calculator">30 - 20</gadget>
<output>10</output>

<result>10</result>