Please help with Practice problems and provide explanations

2. Let Y1, Y2, ...,Yn be a random sample from N01, 02). Let Y\" = 31 L1}?!- and let 52 = i 12.0:- FF. 111 a) Suppose that 02 = 9 and it is desired to have sample mean )7 within 1.5 units of the population mean ,u with probability 0.95. What is the sample size in. required to achieve this? b) Suppose that the variance 02 is unknown and it is desired to have the sample mean within %5 units of the population mean u with probability 0.9. What is the sample size in. required to achieve this