If the sum of the lengths of two adjacent sides of a rectangle is 15 cm, what is the perimeter of the rectangle in cm?
量得一个长方形相邻两条边的长度之和是15厘米，那么这个长方形的周长是多少厘米．
<gadget id="calculator">15 * 2</gadget>
<output>30</output>

<result>30</result>