A population consists of N = 10 primary units, each of which consists of Mi = 6 secondary units. A two-stage sampling design selects 2 primary units by simple random sampling(without replacement) and 3 secondary units from each selected primary unit, also by simple random sampling. The observed values of the variable of interest are 7,5,3 from the first primary unit selected and 4,2,3 from the second primary unit selected. a. Estimate the population mean miu per secondary unit. b. Estimate the variance of the estimator above