The perimeter of a rectangle is 80 cm, the width is 12 cm, and the length is in cm.
一个长方形的周长是80厘米，宽是12厘米，长是多少厘米．
<gadget id="calculator">80 / 2</gadget>
<output>40</output>

<gadget id="calculator">40 - 12</gadget>
<output>28</output>

<result>28</result>