City officials are concerned about the nuisance caused by pigeons around city hall. To emphasize the problem, they hire a team of investigators to estimate the number of pigeons occupying the building. With several different traps a sample of t = 60 pigeons is captured, tagged, and released. One month later, the process is repeated, using n = 60. Suppose s 18 tagged pigeons are observed in the second sample. Estimate N and place a bound on the error of estimation.