The perimeter of a rectangle is 40 cm, and the ratio of length to width is 3:2, what is the length of the rectangle in cm?
一个长方形的周长是40厘米，长与宽的比是3：2，这个长方形的长是多少厘米．
<gadget id="calculator">3 + 2</gadget>
<output>5</output>

<gadget id="calculator">40 / 2 / 5</gadget>
<output>4</output>

<gadget id="calculator">4 * 3</gadget>
<output>12</output>

<result>12</result>