An investigator compares the durability of two different compounds used in the manufacture of a certain automobile brake lining. A sample of 263 brakes using Compound 1 yields an average brake life of 41,270 miles. A sample of 291 brakes using Compound 2 yields an average brake life of 40,579 miles. Assume that the population standard deviation for Compound 2 is 2990 miles. Determine the 90% confidence interval for the true difference between average lifetimes for brakes using Compound 1 and brakes using Compound 2. Find the critical value that should be used in constructing the confidence interval. Construct the 90% confidence interval. Round your answers to the nearest whole number. What is the lower endpoint? What is the upper endpoint?