A firm is experimenting whether to respond to customer complaints via phone or e-mail, and is interested to know how long each method takes from its employees. 219 customers were given phone responses, with a mean of 2 minutes and a standard deviation of 1 minutes. 169 customers were given e-mail responses, with a mean of 5 minutes and a standard deviation of 2 minutes. What is the upper bound of a 99% confidence interval in the difference between the mean response time by phone (condition 1) minus e-mail (condition 2)