Please help me with these questions what do I do?

11. A researcher tries to estimate the population mean by using sufficiently large sample. The probability is 95 that the sample mean X will not differ from the true mean O by more than 5% of standard deviation. How large a sample should be taken? 12. The average of a random sample of size 150 is x =41.1, while the sample standard deviation is s = 3.1 Estimate population mean u with 97% confidence. How large a sample is required if we want to be 97% confident that the sample mean x is within 10% of the population mean u