An investigаtоr wаnts tо estimаte the mean birth weight оf infants born full term to mothers who are 19 years of age and under. It's known that standard deviation of birth weights of full term newborn infants is [a] grams. How many women must be enrolled in the study to ensure that a 95% confidence interval estimate of the mean birth weight of their infants has a margin of error of [b] grams? (round to a whole number)