please explain

A population has standard deviation 6 = 17.1. (a) How large a sample must be drawn so that a W% condence'interval for 51 mi have a margin of error equal to 3.5? Round the critical value to no less than three decimal places. Round the sample size up to the nearest integer. A sample file of E] is needed'to be drawn in order to obtain a 90% condence interval 1with a margin of eer equal to 3.5. (b) If the required condence level were 95%, would the necessary sample size be larger or smaler? (Choose one) 7 . because the condence level is I [Choose one) Y