A researcher wishes to​ estimate, with 9090​% ​confidence, the proportion of adults who have​ high-speed Internet access. Her estimate must be accurate within 44​% of the true proportion. ​a) Find the minimum sample size​ needed, using a prior study that found that 4646​% of the respondents said they have​ high-speed Internet access. ​b) No preliminary estimate is available. Find the minimum sample size needed.