题目

Some people believe that a Robin Hood is at work, others that a wealthy person simply wants to distribute his or her fortune before dying. But the donator who started sending envelopes with cash to deserving causes，accompanied by an article from the local paper, has made a northern German city believe in fairytales (童话).        The first envelope was sent to a victim support group. It contained 0,000 with a cutting from the Braunschiveiger Zeitung about how the group supported a woman who was robbed of her handbag; similar plain white anonymous envelopes, each containing 0,0一根铁丝长12.56米，正好在现代战争圆形圈上绕满50周，这个圆圈的半径是多少？