A researcher wishes to estimate, with % confidence, the population proportion of adults who think Congress is doing a good or excellent job. Her estimate must be accurate within % of the true proportion. (a) No preliminary estimate is available. Find the minimum sample size needed. (b) Find the minimum sample size needed, using a prior study that found that % of the respondents said they think Congress is doing a good or excellent job. (c) Compare the results from parts (a) and (b). (a) What is the minimum sample size needed assuming that no prior information is available? n 1068 (Round up to the nearest whole number as needed.)