12. Consider the following weighted averages of independent random variables X], X2, X; all with m # and variance of: 1 #1 = =Xit=X,t-X3 3 3 3 Xi+-X2+ -13 4 CIN PI e3 = X1 + X2 + (a) Find E], E[ez], and E[es] (b) Are 61, 61, and 6 unbiased for ? Explain. (c) Find the variance for 61, 61, and e1. (d) If you had to use one of the above unbiased estimators, which would you pick? Explain