Please pay attention to the format of the question. If you can't answer it, please don't copy and paste from a similar answer (which doesn't apply) or I will give it a thumbs down.
Given yi = Po + β(xi - μ) + εi, derive the conditional variance of the OLS estimator of β. Construct an estimator of the conditional variance. Is this estimator unbiased for the conditional variance? Note: conditional means "conditional on x".