If the width of a rectangle is 20 decimeters and the length is twice the width, what is its perimeter?
一个长方形的宽是20分米，长是宽的2倍，那么它的周长是多少米？
<gadget id="calculator">20 * 2</gadget>
<output>40</output>

<gadget id="calculator">40 + 20</gadget>
<output>60</output>

<gadget id="calculator">60 * 2</gadget>
<output>120</output>

<result>120</result>