Step 1: Write second polynomial below the first one. Making sure like terms are lined up.
$$ \begin{array}{lrr} & -2x & \\ \color{red}{ - } & -x & 2 \\ \hline \end{array} $$Step 2: Change ALL the signs in the second row.
$$ \begin{array}{lrr} & -2x & \\ \color{red}{ - } & x & -2 \\ \hline \end{array} $$Step 3: Combine like terms (add each column):
$$ \begin{array}{lrr} & -2x & \\ \color{red}{ - } & x & -2 \\ \hline & -3x & 2 \end{array} $$