The lifetime (in hours) of a 60-watt light bulb is a random variable that has a Normal distribution with standard deviation 30. A random sample of 25 bulbs put on test produced a sample mean lifetime of 1038. The 92% confidence interval estimate for the mean lifetime, μ, is (1027.5, 1048.5). If it were desired to cut the confidence interval to half its length while keeping the same 92% level, what size sample would be required to achieve this?