Estimating Mean

I am having difficulty with this question and was wondering if I can get some help?

The manufacturer of official NFL footballs uses a machine to inflate the new balls to a pressure of 13.5 pounds. When the machine is properly calibrated, the mean inflation pressure is 13.5 pounds, but uncontrollable factors cause the pressures of individual balls to vary randomly from about 13.3 to 13.7 pounds. For quality-control purpose, the manufacturer wishes to estimate the mean inflation pressure to within 0.025 pound of its true value with a 99% confidence interval. What sample size should be used?

The formula I believe I'm suppose to use is n = (n*standard deviation/e)^2. However, I don't see the standard deviation anywhere in the problem. Is there some way I need to calculate it?\