The grades of a class of 9 students on a midterm report $(x)$ and on the final examination $(y)$ are as follows:
$$
\begin{array}{c|ccccccccc}
x & 77 & 50 & 71 & 72 & 81 & 94 & 96 & 99 & 67 \\
\hline y & 82 & 66 & 78 & 34 & 47 & 85 & 99 & 99 & 68
\end{array}
$$
(a) Estimate the linear regression line.
(b) Estimate the final examination grade of a student who received a grade of 85 on the midterm report.