Data were collected on the amount spent by 100 customers for lunch at a major Houston restaurant. The mean amount spent for lunch is $21.52. Based upon past studies the population standard deviation...

Data were collected on the amount spent by 100 customers for lunch at a major Houston restaurant. The mean amount spent for lunch is $21.52. Based upon past studies the population standard deviation is known to be $6. At 99% confidence, what is the margin of error?