In Problems 9-16, find the indicated matrices, if possible.

\[[\mathrm{A}]=\left[\begin{array}{rr}1 & 2 \\4 & 0 \\-1 & 3 \\2 & 1 \end{array}ight] \quad[\mathrm{B}]=\left[\begin{array}{rr}4 & 2 \\-1 & 3\end{array}ight]\]\[\begin{array}{lll}{[\mathrm{C}]=\left[\begin{array}{llll}1 & 0 & 0 & 0 \\0 & 1 & 0 & 0 \\0 & 0 & 1 & 0 \\
0 & 0 & 0 & 1 \end{array}ight]} & {[\mathrm{D}]=\left[\begin{array}{rrrr}4 & 1 & 3 & 6 \\
-1 & 0 & -2 & 3 \end{array}ight]} \\{[\mathrm{E}]=\left[\begin{array}{rrr}1 & 0 & 2 \\3 & -1 & 2 \\4 & 1 & 0 \end{array}ight]} & {[\mathrm{F}]=\left[\begin{array}{rrr}
1 & 4 & 0 \\3 & -1 & 2 \\-2 & 1 & 5 \end{array}ight]} \\{[\mathrm{G}]=\left[\begin{array}{rrr}
8 & 1 & 6 \\3 & 5 & 7 \\4 & 9 & 2 \end{array}ight]} &\end{array}\]

a. \([F][G]\)

b. \([\mathrm{G}][\mathrm{F}]\)