Firstly, your rank is not correct..
The row reduced echleon form of the given matrix should be a
try doing it again..
Compute the rank and nullity of the matrix A and state what this implies about the existence and/or uniqueness of solutions x of Ax=b.
A = [1 1 3]
1 2 3
3 2 1
Sol: Reduced row echelon form = [1 0 -1]
0 1 2
0 0 0
Therefore, Rank(A)=2, and Nullity (A) = 1. But I don't get the second part though. Does it mean there's only one solution?