Subtract polynomials: $ \, \color{blue}{ 20s^7+360s^6+2700s^5+11200s^4+27480s^3+37440s^2+21600s } \, $ , $ \, \color{orangered}{ s^7+36s^6+512s^5+3634s^4+13287s^3+22730s^2+12600s }$.

$$ \left( \color{blue}{20s^7+360s^6+2700s^5+11200s^4+27480s^3+37440s^2+21600s} \right) - \left( \color{orangered}{s^7+36s^6+512s^5+3634s^4+13287s^3+22730s^2+12600s} \right) = 19s^7+324s^6+2188s^5+7566s^4+14193s^3+14710s^2+9000s $$

Step 1: Write second polynomial below the first one. Making sure like terms are lined up.

$$ \begin{array}{lrrrrrrr} & 20s^7 & 360s^6 & 2700s^5 & 11200s^4 & 27480s^3 & 37440s^2 & 21600s \\ \color{red}{ - } & s^7 & 36s^6 & 512s^5 & 3634s^4 & 13287s^3 & 22730s^2 & 12600s \\ \hline \end{array} $$

Step 2: Change ALL the signs in the second row.

$$ \begin{array}{lrrrrrrr} & 20s^7 & 360s^6 & 2700s^5 & 11200s^4 & 27480s^3 & 37440s^2 & 21600s \\ \color{red}{ - } & -s^7 & -36s^6 & -512s^5 & -3634s^4 & -13287s^3 & -22730s^2 & -12600s \\ \hline \end{array} $$

Step 3: Combine like terms (add each column):

$$ \begin{array}{lrrrrrrr} & 20s^7 & 360s^6 & 2700s^5 & 11200s^4 & 27480s^3 & 37440s^2 & 21600s \\ \color{red}{ - } & -s^7 & -36s^6 & -512s^5 & -3634s^4 & -13287s^3 & -22730s^2 & -12600s \\ \hline & 21s^7 & 396s^6 & 3212s^5 & 14834s^4 & 40767s^3 & 60170s^2 & 34200s \end{array} $$

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