Stuck, need a bit of help

[nternet Viewing A researcher wishes to estimate the average number of minutes per day a person spends on the Internet. How arge a sample must she select if she wishes to be 95% condent that the population mean is within 13 minutes of the sample nean? Assume the population standard deviation is 40 minutes. Round your nal answer up to the next whole number. The researcher needs a sample of at least D people