$\text{a)}$

$\sqrt{4}\cdot \sqrt{25}=\sqrt{100}=10$

$\sqrt{2}\cdot \sqrt{50}=\sqrt{100}=10$

$\sqrt{18}\cdot \sqrt{2}=\sqrt{36}=6$

$\sqrt[3]{4}\cdot \sqrt[3]{54}=\sqrt[3]{216}=6$

$\sqrt[3]{3}\cdot \sqrt[3]{9}=\sqrt[3]{27}=3$

$\sqrt[3]{-2}\cdot \sqrt[3]{32}=\sqrt[3]{-64}=-4$

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$\text{b)}$

$\sqrt{27}\cdot \sqrt{3}=\sqrt{81}=9$

$\sqrt{0,72}\cdot \sqrt{2}=\sqrt{1,44}=1,2$

$\sqrt[3]{2}\cdot \sqrt[3]{-4}=\sqrt[3]{-8}=-2$

$\sqrt[3]{24}\cdot \sqrt[3]{9}=\sqrt[3]{216}=6$

$\sqrt[3]{-0,02}\cdot \sqrt[3]{1350}=\sqrt[3]{-27}=-3$