A square piece of paper has a perimeter of 40 cm, what is the perimeter of a rectangle when folded in half?
一张正方形纸，周长是40厘米，对折成一个长方形的周长是多少．
<gadget id="calculator">40 / 4</gadget>
<output>10</output>

<gadget id="calculator">10 * 3</gadget>
<output>30</output>

<result>30</result>