please explain

Call me: A sociologist wants to construct a 90% confidence interval for the proportion of children aged 8-10 living in New York who own a cell phone. Part 1 of 3 (a) A survey by the National Consumers League taken in 2012 estimated the nationwide proportion to be 0.30. Using this estimate, what sample size is needed so that the confidence interval will have a margin of error of 0.03? A sample of | 632 children aged 8-10 living in New York is needed to obtain a 90% confidence interval with a margin of error of 0.03 using the estimate 0.30 for p. Part: 1 / 3 Part 2 of 3 (b) Estimate the sample size needed if no estimate of p is available. A sample of children aged 8-10 living in New York is needed to obtain a 90% confidence interval with a margin of error of 0.03 when no estimate of p is available