How large a sample size is needed to estimate the mean annual income of people in a certain? county, correct to within?$500with probability? 0.99? No information is available about the standard...

How large a sample size is needed to estimate the mean annual income of people in a certain? county, correct to within?$500with probability? 0.99? No information is available about the standard deviation of their income. It is estimated that nearly all of the incomes fall between? $0 and?$120,000and that this distribution is approximately? bell-shaped.