The lifespan of brand A batteries is Normally distributed with a mean of 108 hours and a standard deviation of 12.5 hours. The lifespan of brand B batteries is Normally distributed with a mean of 92 hours and a standard deviation of

15.1 hours. A quality control specialist selects a random sample of 25 of each type of battery and calculates the

sample mean lifespan for each brand. Let 5, -ē, be the difference in the sample mean lifespan for each brand of

battery. What is the mean of the sampling distribution of the difference in sample means?

Do not round your answer.