What the answer to number 7

Answer:
Step-by-step explanation:
Focus on #7. Let's combine the first two matrices inside round parentheses.
We get
-2 - 1
4 + 3
and so the original problems becomes
-3 4
3( [ ] + [ ] )
7 2
Combining the two matrices, we get the following:
1 3
3([ ]) = [ ]
9 9