No wrong numbers

Mr. Green has a garage in Silbury. Now he has just bought another garage in Pinhurst. Pinhurst is only five miles from Silbury, but Mr. Green cannot get a telephone for his new garage, so he has just bought twelve pigeons. Yesterday, a pigeon carried the first message from Pinhurst to Silbury. The bird covered the distance in three minutes. Up to now, Mr. Green has sent a great many requests for spare parts and other urgent messages from one garage to the other. In this way, he has begun his own private 'telephone' service.