Let U be a population of size N which is partitioned into 2 strata U1 and U2, of size N1 and N2, respectively. Let gm = Nfl Zia]! yi and 3w 2 N;1 21.6% y;- denote the stratum means of a survey variable y in both strata. In stratum h, h = 1, 2, we select a simple random sample without replacement Sh, of size m, h = 1, 2. The sample selection in Stratum 1 is independent from the sample selection in Stratum 2. (a) Suppose that we want to estimate the difference D = gm yU2. Propose an unbiased estimator of D (call it 13) and determine its variance (b) Suppose that we want to estimate the product P 2 gm >