\(\mathrm{M}^{-1} = \begin{bmatrix} -1 & 0 \\ 8 & 1 \end{bmatrix}\)
First row, first column: \(\boxed{1}\)
First row, second column: \(\boxed{0}\)
Second row, first column: \(\boxed{0}\)
Second row, second column: \(\boxed{1}\)
Thus, \(\mathrm{M}^{-1} \mathrm{M} = \mathrm{I}\).