There is a race car with a front wheel diameter of 7 decimeters and a rear wheel radius of 7 decimeters. Its front wheel rolls 30 times on the ground, how many times does the rear wheel roll on the ground?
有一种赛车前轮直径7分米，后轮半径7分米，它的前轮在地上滚动30圈，后轮在地上滚动多少圈？
<gadget id="calculator">3.14 * 7 * 30</gadget>
<output>659.4</output>

<gadget id="calculator">3.14 * 7 * 2</gadget>
<output>43.96</output>

<gadget id="calculator">659.4 / 43.96</gadget>
<output>15</output>

<result>15</result>