The television picture tubes of manufacturer A have a mean lifetime of 6.5 years and a standard deviation of 0.9 years, while those of manufacturer B have a mean lifetime of 6.0 years and a standard deviation of 0.8 years. Suppose a random sample of 36 tubes from manufacturer A will have a mean lifetime ¯ X₁ and a random sample of 49 tubes from manufacturer B will have a mean lifetime ¯ X₂. These two random samples are independent

Find the sampling distribution of ¯ X₁ − ¯ X₂