If the minute hand on a clock face is 9 cm long, what is the length of the arc of the minute hand in 20 minutes?
一钟面上的分针长9厘米，则分针在20分钟内其针尖化过的弧线长为多少厘米．
<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">2 * 3.14 * 9 * (1/3)</gadget>
<output>18.84</output>

<result>18.84</result>