Here's what I would have submitted:

Question 1:

Clearly 0=A0 is in col A.
If u=Ax and v=Ay are in col A, then u+v=Ax+Ay=A(x+y) which is in col A.
If u=Ax in col A and c a scalar, then cu=cAx=A(cx) which is in col A.
Thus col A is a subspace.



Question 2:

[-2 ] [-2]
[ 1 ] [-2]
[ 1 ],[ 0]
[ 0 ] [ 1]
[ 0 ] [ 0]




Question 3:

[ 1]  [5]  [4]
[ 4]  [1]  [3]
[-1], [5], [3]
[-2]  [4]  [1]
[-2]  [2]  [3]