For Q.1,

Since the question only asks about "confidence interval for thepopulation mean" and you already know that the population mean is 30 and population standard deviation is 8,then, the C.I. is just:

Upper limit = 30 + 1.645 * 8

Lower limit = 30 - 1.645 * 8,

in my opinion, there is no need to divide the std by anything.