Find the bases for the column, row, and null spaces of the matrix

[1 -2 -1 3 ]

[4 -7 1 12]

[3 -5 2 9]

I got the basis of row space to be:

{(1 0 9 3)^T, (0 1 5 0)^T}

So that gives me the system of equations:

{x1 + 9x3 + 3x4 = 0

{x2 + 5x3 = 0

Now I'm lost. I can't seem to manipulate this to get the null space. Any hints?