For exercise a, we have $-2 \sqrt{7 z^{3}}$ and $3 \sqrt{14 z^{8}}$. We can multiply the numbers outside the square roots, which gives us $-6$. Inside the square roots, we have $7 z^{3}$ and $14 z^{8}$. We can multiply these together to get $98 z^{11}$.
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