Suppose that the standard deviation of an observation in a given population is known to be $\sigma = 15$.
How many observations in a sample is needed to estimate $\overline{x}$ (the mean of the sample) within $±5$ of the population mean $ \mu$ with $99$% confidence?
This has me stumped I don't know where to start, any assistance in finding the sample mean $\overline{x}$, population mean $ \mu$ how to find $±5$ of that mean and amount of observations needed... would be appreciated!