The true average tread lives of two competing brands of radial tires (brand X and brand Y) are known to be normally distributed. The standard deviation of brand X tires is known to be 2200, and the standard deviation of brand Y tires is known to be 1900. A sample of 45 brand X tires results in a sample mean of 42,500 and sample standard deviation of 2450. A sample of 45 brand Y tires results in a sample mean of 40,400 and sample standard deviation of 2150. Find a 95% confidence interval for the difference in the true means, mean of X minus mean of Y.