If the length of a rectangle is 15 cm and its length is 3 times its width, what is its perimeter in cm?
一个长方形的长是15厘米，且长是宽的3倍，则它的周长是多少厘米．
<gadget id="calculator">15 / 3</gadget>
<output>5</output>

<gadget id="calculator">15 + 5</gadget>
<output>20</output>

<gadget id="calculator">20 * 2</gadget>
<output>40</output>

<result>40</result>