please give me the steps:

1 Minimum variance unbiased estimator for Poisson data Let Y1, ..., Yn be IID Poisson ()) random variables. Argue that Y, the sample mean, is a sufficient statistic for A by using the factorization criterion. Assuming that Y is a complete sufficient statistic, explain why Y is the minimum variance unbiased estimator. (Hint: Use the corollary of the Lehmann-Scheffe theorem from Lecture 11.)