$\displaystyle \begin{pmatrix} -1 & -2 \\9 & 4\end{pmatrix}$$\displaystyle \begin{pmatrix} 1-3k & -k \\9k & 3k+1\end{pmatrix}$

What does that equal? Thanks in advance.

(EDIT: Sorry, I didn't realise that I was on Calculus forum hence posted incorrect thread. Thought I was in Urgent Homework Help forum.)