The ratio of the lengths of the sides of a triangle is 2:2:3, and the perimeter is 42 cm, what is the longest side in cm?
三角形三边长度之比是2：2：3，周长是42厘米，则最长的边是多少厘米．
<gadget id="calculator">2 + 2 + 3</gadget>
<output>7</output>

<gadget id="calculator">3 / 7</gadget>
<output>3/7 = around 0.428571</output>

<gadget id="calculator">42 * (3/7)</gadget>
<output>18</output>

<result>18</result>