Suppose that \(Y\) and \(X\) are related by the regression \(Y=1.0+2.0 X+u\). A researcher has observations on \(Y\) and \(X\), where \(0 \leq X \leq 20\), where the conditional variance is \(\operatorname{var}\left(u_{i} \mid X_{i}=x\right)=1\) for \(0 \leq x \leq 10\) and \(\operatorname{var}\left(u_{i} \mid X_{i}=x\right)=16\) for \(1010\) ? Why?