I would like to know how can I solve question a) and b) with the calculator TI 84

A researcher wishes to estimate the proportion of adults who have high-speed Internet access, What size sample should be obtained if she wishes the estimate to be within 0.04 with 95% condence it (a) she uses a previous estimate of 0.56? (b) she does not use any prior estimates? (a) n = ID (Round up to the nearest integer.)