Step 1: First we have to write polynomials in descending order.
$$ \begin{aligned} P(x) &= -x-8 \\ Q(x) &= 1823x+9 \\ \end{aligned} $$Step 2: Write second polynomial below the first one. Making sure like terms are lined up.
$$ \begin{array}{lrr} & -x & -8 \\ \color{red}{ - } & 1823x & 9 \\ \hline \end{array} $$Step 3: Change ALL the signs in the second row.
$$ \begin{array}{lrr} & -x & -8 \\ \color{red}{ - } & -1823x & -9 \\ \hline \end{array} $$Step 4: Combine like terms (add each column):
$$ \begin{array}{lrr} & -x & -8 \\ \color{red}{ - } & -1823x & -9 \\ \hline & 1822x & 1 \end{array} $$