Problems $4 I-48$. compute the image under $T$ of $\overrightarrow{\mathrm{u}}$, and find the vector(s), if any, that are mapped to $\overrightarrow{\mathbf{w}}$.
$T\left(u_1, u_2, u_3\right)=\left(u_1, u_2, u_1+u_3\right)$,
$$
\overline{\mathbf{u}}=(1,2,1), \quad \overrightarrow{\mathbf{w}}=(0,0,1)
$$