A light bulb manufacturer wants to compare the mean lifetimes of two of its light bulbs, model A and model B. Independent random samples of the two models were taken. Analysis of 9 bulbs of model A showed a mean lifetime of 1380 hours and a standard deviation of 96 hours. Analysis of 13 bulbs of model B showed a mean lifetime of 1291 hours and a standard deviation of 84 hours. Assume that the populations of lifetimes for each model are normally distributed and that the variances of these populations are equal. Construct a 90% confidence interval for the difference , J, between the mean lifetime uj of model A bulbs and the mean lifetime J, of model B bulbs. Then find the lower limit and upper limit of the 90% confidence interval. Carry your intermediate computations to at least three decimal places. Round your responses to at least two decimal places. (If necessary, consult a list of formulas.) Lower limit: X ? Upper limit