A sample of four tires is taken from alot of brand-A tires. Another sample of four tires is taken from a lot of brand-B tires. These tires are tested for amount of wear, for 24,000 miles of driving on an eight-wheel, truck, when the tires are rotated every 1000 miles. The tires are weighed before and after the test. The loss in weight, expressed as the percentage of intial weight is used as a measure of wear. For the sample Brand-Atires, it is found that X_A = 180, S_A = 1.3: for the brand B tires X_B =19.4 and S_B = 1.5. Assuming approximately normal distributions having equal variances for percent wear of tires each brand under test conditions, find a 95% confidence interval for muA - muB