Independent random samples are taken from the output of two machines on a production line. The weight of each item is of interest. size 36 is taken, with sample mean weight of 120 grams and a sample variance of 4. From the second machine, a sample of size 64 is taken, with a sample mean weight of 130 grams and a sample variance of 5. It is assumed that the weights of the items from the first machine are normally distributed with mean (mu1) and variance (sigma^2) and that the weights of items from the second machine are normally distributed with mean (mu2) and variance 9sigma^2) (that is, the variances are assumed to be equal). Find a 99% confidence interval for mu1-mu2, the difference in population means when it is known in advance that the population variances are 4 and 5 respectively.