i wonder how to solve this question

(Optional) Let Yj = x;B+6;, j =1,2, ... be a simple linear regression model, where {In}n>1 is a given sequence of real numbers, B E R is the regression parameter, and {En}21 is a sequence of i.i.d. random variables with E(61) = 0 and E() = 02 E (0, oo). The ordinary least squares estimators of B based on Y1, . .., Yn is given by n Bn = n > 1, a2 j=1 where a? = _ x7. Suppose that the sequence {In }n>1 satisfies max max 1