how do I calculate part 2?

(Fox 6.9) Suppose that the \"true\" model generating a set of data is Y : a + [3X1 + e. A researcher ts the model Y = o: + {31X 1 + 5'ng + 6, which includes the explanatory variable X2,Athat is the true value of ,82 is 0. Had the researcher t the (correct) simple regression model, the variance of 51 would have been (using the simple regression formula) V031) : 03/ Z(X,;1 X1)2. 1. Is the model Y : o: + [3le + {3'ng + 6 wrong? In other words, is Bl for this model a biased estimator of ,81?(2 points) 2. What is the variance of {3'1 in the second model? (4 points) 3. Considering (a) and (b), What is the cost of including the irrelevant explanatory variable X2? How does this compare to the cost of failing to include a relevant explanatory variable? (2 points)