The amount of material used in making a custom sail for a sailboat is normally distributed with a standard deviation of 64 square feet.

The amount of material used in making a custom sail for a sailboat is normally distributed with a standard deviation of 64 square feet. For a random sample of 15 sails, the mean amount of material used is 912 square feet. Which of the following represents a 99% confidence interval for the population mean amount of material used in a custom sail? 

A) 912 ± 49.2 

B) 912 ± 42.6 

C) 912 ± 44.3 

D) 912 ± 46.8