The circumference of two circles A and B differ by 18.84 cm, what is the difference in their radii?
甲、乙两个圆的周长相差18.84厘米，它们的半径相差多少．
<gadget id="calculator">18.84 / 3.14 / 2</gadget>
<output>3</output>

<result>3</result>