A fast food restaurant executive wishes to know how many fast food meals teenagers eat each week

A fast food restaurant executive wishes to know how many fast food meals teenagers eat each week. They want to construct a 85% confidence interval with an error of no more than 0.06. A consultant has informed them that a previous study found the mean to be 4.9 fast food meals per week and found the standard deviation to be 0.9. What is the minimum sample size required to create the specified confidence interval?