If the length of an arc is equal to the circumference of a circle A, and the radius of the circle where this arc is located is three times the radius of circle A, what is the central angle subtended by this arc in degrees?
一段弧长与一个圆A的周长相等，且这段弧所在的圆的半径是圆A半径的3倍，则这段弧所对的圆心角是多少度．
<gadget id="calculator">360 / 3</gadget>
<output>120</output>

<result>120</result>