A manufacturer claims that the average tensile strength of thread A exceeds the average tensile strength of thread B by at least 12 kilograms. To test this claim, 50 pieces of each type of thread are...

A manufacturer claims that the average tensile strength of thread A exceeds the average tensile strength of thread B by at least 12 kilograms. To test this claim, 50 pieces of each type of thread are tested under similar conditions. Type A thread had an average tensile strength 86.7 kgs with a standard deviation of 6.28 kgs, while type B thread had an average tensile strength of 77800 grams with variance of 31.4721 kgs. Test the manufacturer claims at 5% level of significance.