Fitted line between uncorrelated variables

Random variables $X$ and $Y$ have $\mathbb{E}X=6$, $\operatorname{Var}X=2$, $\mathbb{E}Y=8$, $\operatorname{Var}Y=10$ and zero covariance. The population least-squares line $Y=aX+b$ is fitted. Compute $a+b$.

$8$. The slope is $\operatorname{Cov}(X,Y)/\operatorname{Var}X=0$, so the best line is flat at the mean of $Y$: $a=0$, $b=8$.