A stereo manufacturer claims his top-of-the-line turntable has an average lifespan of more than 15 years. When asked to provide evidence that supports this claim, he obtains from his files the names of 15 customers who have purchased this high quality turntable and asks each
how long their turntables ran before needing replacement. From these 15 measurements he computes and average lifespan of 17 years with a
variance of 4 years. The value of the test statistic (rounded off to two decimals) is:​