When did Mr Cobble bring out the knot in Maniac Magee?

The knot appeared one day and Mr.Cobble thought he could use it to get buisness. Whoever untied it got their picture in the newspaper and a free large Pizza every week for a year. No one could untie it until Maniac came along. Maniac was good with knots and untied it in a day. He was a hero.