I already got my own answer, and this is from a practice section of the book with the answer at bottom of book. but my answer and the book answer didnt match. so i copied and pasted the question below so can you show how you solve this from A to Z so i can see if i could catch where i was wrong?

You wish to estimate the mean number of travel days per year for salespeople. The mean of a small pilot study was 150 days, with a standard deviation of 44 days.

If you want to estimate the population mean within 10 days, how many salespeople should you sample? Use the 99% confidence level. (Usez Distribution Table.)(Round up your answer to the next whole number.)

Number of outside salepeople =