6. Suppose you collect your regression data from two companies. One has better quality than the other. So you model the data from the rst company by yi N N(+1'i, an) independently for i = 1, ".111, and the data from the second one by ya- N N( + ,81 m5, 252) independently for i = m + 1, ...,n1+ Hg. The data from the two companies are also independent from each other. (a) Find the NILE for (g, 51). (b) Find the mean of the MLE. (c) Find the variance of the MLE. (d) Find the joint distribution of the MLE