Step 1: First we have to write polynomials in descending order.

$$ \begin{aligned} P(x) &= 20m-3 \\ Q(x) &= 3m+4 \\ \end{aligned} $$

Step 2: Write second polynomial below the first one. Making sure like terms are lined up.

$$ \begin{array}{lrr} & 20m & -3 \\ \color{red}{ - } & 3m & 4 \\ \hline \end{array} $$

Step 3: Change ALL the signs in the second row.

$$ \begin{array}{lrr} & 20m & -3 \\ \color{red}{ - } & -3m & -4 \\ \hline \end{array} $$

Step 4: Combine like terms (add each column):

$$ \begin{array}{lrr} & 20m & -3 \\ \color{red}{ - } & -3m & -4 \\ \hline & 23m & 1 \end{array} $$

Polynomial Operations Calculator