Step 1: Write second polynomial below the first one. Making sure like terms are lined up.
$$ \begin{array}{lrrrrr} & & 2z^{13} & 11z^{10} & 7z^7 & 9z^5 \\ \color{red}{ - } & 7z^{14} & & -7z^{10} & 7z^7 & 4z^5 \\ \hline \end{array} $$Step 2: Change ALL the signs in the second row.
$$ \begin{array}{lrrrrr} & & 2z^{13} & 11z^{10} & 7z^7 & 9z^5 \\ \color{red}{ - } & -7z^{14} & & 7z^{10} & -7z^7 & -4z^5 \\ \hline \end{array} $$Step 3: Combine like terms (add each column):
$$ \begin{array}{lrrrrr} & & 2z^{13} & 11z^{10} & 7z^7 & 9z^5 \\ \color{red}{ - } & -7z^{14} & & 7z^{10} & -7z^7 & -4z^5 \\ \hline & 7z^{14} & 2z^{13} & 4z^{10} & 14z^7 & 13z^5 \end{array} $$