Solution
= Solution
The OLS normal equation with an intercept gives $\hat\beta=S_{XY}/S_{XX}$. By the law of large numbers it tends to $\operatorname{Cov}(X,Y)/\operatorname{Var}X$. Here $X=Z+U+\epsilon_X$ and $Y=X+U+\epsilon_Y$, so the <limit> is $(3+1)/3=4/3$, showing upward confounding bias.