Problems $4 I-48$. compute the image under $T$ of $\overrightarrow{\mathrm{u}}$, and find the vector(s), if any, that are mapped to $\overrightarrow{\mathbf{w}}$.
$T\left(u_1, u_2\right)=\left(u_2, u_1, u_1+u_2\right)$,
$$
\overline{\mathbf{u}}=(1,2), \quad \overrightarrow{\mathbf{w}}=(2,1,3)
$$