For a tractor, the diameter of the rear wheel is twice that of the front wheel, and the rear wheel rolls 6 times, how many times does the front wheel need to roll.
一台拖拉机，后轮直径是前轮的2倍，后轮滚动6圈，前轮要滚动多少圈．
<gadget id="calculator">2 * 3.14 * 6</gadget>
<output>37.68</output>

<gadget id="calculator">37.68 / 3.14</gadget>
<output>12</output>

<result>12</result>