The production manager at a battery factory wants to determine whether there is any difference in the mean life expectancy of batteries manufactured on two different types of machines. A random sample of 21 batteries from machine 1 indicates a mean of 250 hours and a standard deviation of 75 hours, and a similar sample of 21 from machine 2 indicates a mean of 242 hours and a standard deviation of 90 hours. Using the 1% level of significance, is there any evidence of a difference in the mean life of batteries produced by the two types of machines?