An independent rating service is trying to determine which of two film-developing shops has quicker service. Over a period of 12 randomly selected times, the average waiting period to develop a 24-exposure roll sold at Speedy Development is 58 minutes with standard deviation 3.5 minutes. The average waiting period at the Shutterbug to develop a 24-exposure roll over a period of 8 randomly selected times is 53 minutes with standard deviation 4.9 minutes. Using a 1% level of significance, can we say that there is a difference in the average waiting time between the two shops? Find the critical value(s).