Here's what I would have submitted:

Question 1:

[0 1 0]
[1 0 0]
[2 0 1]



Question 2:

Augment with the identity
[1  3 0  1 0 0]
[3 10 0  0 1 0]
[0 -3 1  0 0 1]
Subtract 3*row 1 from row 2
[1  3 0  1 0 0]
[0  1 0 -3 1 0]
[0 -3 1  0 0 1]
Add 3*row 2 to row 3
[1 3 0  1 0 0]
[0 1 0 -3 1 0]
[0 0 1 -9 3 1]
Subtract 3*row2 from row 1
[1 0 0 10 -3 0]
[0 1 0 -3  1 0]
[0 0 1 -9  3 1]
        [10 -3 0]
So N^-1=[-3  1 0]
        [-9  3 1]




Question 3:

[I  0 0]
[0  I 0]
[-A 0 I]