help please ??

Birthweight is studied because low birthweight is an indicator of infant mortality. A study of babies in Norwayr published in the International Journal of Epidemiology shows that birthweight of fullterm babies {37 weeks or more of gestation) are very close to normallj,r distributed with a mean of 3600 g and a standard deviation of 601] g. Suppose that Melanie is a researcher who wishes to estimate the mean birthweight of fullterm babies in her hospital. What is the minimum number of babies should she sample if she wishes to be at least 95% condent that the mean birthweight of the sample is within 180 g of the the mean birthweight of all babies? Assume that the distribution of birthweights at her hospital is normal with a standard deviation of 600 g