The perimeter of a rectangle is 40 meters, and the ratio of length to width is 4:1. What is its length in meters?
一长方形的周长是40米，长和宽的比是4﹕1，它的长是多少米米．
<gadget id="calculator">40 / 2</gadget>
<output>20</output>

<gadget id="calculator">4 + 1</gadget>
<output>5</output>

<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">20 * (4/5)</gadget>
<output>16</output>

<result>16</result>