The Mean Number of Travel Days Per Year for the Outside

The mean number of travel days per year for the outside salespeople employed by hardware
Distributors is to be estimated. The 0.90 degree of confidence is to be used. The mean of a small
Pilot study was 150 days, with a standard deviation of 14 days. If the population mean is to be
Estimated within two days, how many outside salespeople should be sampled?

A) 133
B) 452
C) 511
D) 2,100