I have the following problem:

I have 2 3x3 matrices, on called M and the other N^-1 (this one has a few unknown numbers, k). I am asked to find the following:

(MN)^-1. Now we have NOT learned how to do the inverse of 3x3 matrices yet, so there must be some other way of solving this...but how?

M=

(3 0 8

0 2 0

1 0 4)

and N^-1=

(1 -2 3

3 k 0

2 4 k)

Please help...