For a tractor, the diameter of the rear wheels is twice that of the front wheels, and the rear wheels turn 4 times, how many times the front wheels turn.
一台拖拉机，后轮直径是前轮的2倍，后轮转动4圈，前轮转动多少圈圈．
<gadget id="calculator">4 * 2</gadget>
<output>8</output>

<result>8</result>