A rectangle is 10 cm wide and twice as long as it is wide, what is the perimeter of the rectangle?
一个长方形宽10厘米，长是宽的两倍，求这个长方形的周长多少．
<gadget id="calculator">10 * 2</gadget>
<output>20</output>

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

<gadget id="calculator">30 * 2</gadget>
<output>60</output>

<result>60</result>