Not Sure how to even start this one

The mean number of travel days per year for salespeople employed by hardware distributors needs to be estimated with a 98% degree of confidence. For a small pilot study the mean was 150 days and the standard deviation was 12 days. If the population mean is estimated within four days, how many salespeople should be sampled?

Re: Not Sure how to even start this one

m=150

s=12 =sample sd

$\displaystyle \sigma =s\sqrt{n}$ = population sd

$\displaystyle z_{.98}=2.3263$ two-sided normal distribution z-value

$\displaystyle -\sigma z_{.98}\leq m\pm 4\leq \sigma z_{.98}$

$\displaystyle m+4\leq s z_{.98}\sqrt{n}$

Solve to obtain:

n > 30