From the matrix equation `AX=B` find the matrix `X`, given that $ A = \begin{bmatrix} 1 & -1 & 0 \\ 0 & 1 & -1 \\ 1 & 1 & 1 \end{bmatrix} $ and $ B = \begin{bmatrix} 2 \\ 1 \\ 7 \end{bmatrix}$