i'm having trouble demonstrate the b) question, if u please help me would be really apreciated:

(this exercise is on the upload photo too)

1. Consider the model

Yi = Xi + ui; i = 1; :::;N

where ui satis…es the usual hypotheses.

(a) Derive by OLS the estimator of the parameter :

(b) Show that the estimador obtained in (a) is unbiased. (Hint: Compute the

expected value of the estimator.)

my resolution is on the anex file, also please tell me the right way to do it the b) correctly.

thanks and sorry for my english.