To assess the accuracy of a laboratory scale, a standard weight that is known to weigh 1 gram is repeatedly weighted a total of n times and the meanx of the weightings is computed. Suppose the scale readings are normally distributed with unknown mean and standard deviation = 0.01 g. How large should n be so that a 95% confidence interval for has a margin of error of 0.0001?

I'm so confused on how to find n. I know the answer for n = 38,416, I'm just not sure how to get that answer.

Thanks!