Statistics question:

we intended to estimate the average driving time of a group of commuters from a previous study, we believe that the average time is 42 minutes with a standard deviation of 12 minutes. we want of 99 percent confidence interval to have a margin of error or no more than plus or minus 3 minutes. what is the smallest sample size we should consider?

ok, so
n = 42 minutes
stand. deviation = 12
confidence interval = .99
alpha = .005
z-score = +- 2.575 (i think)
and e = +-3

what?