For a tractor, the diameter of the rear wheel is 4 times the diameter of the front wheel, and the rear wheel rolls 4 times, how many times the front wheel rolls.
一台拖拉机，后轮直径是前轮直径的4倍，后轮滚动4圈，前轮滚动多少圈．
<gadget id="calculator">4 * 4</gadget>
<output>16</output>

<result>16</result>