a)

$\sqrt{49\cdot 36}=\sqrt{49}\cdot \sqrt{36}=7\cdot 6=42$  

 

$\sqrt{16\cdot 25\cdot 81}=\sqrt{16}\cdot \sqrt{25}\cdot \sqrt{81}=4\cdot 5\cdot 9=180$  

 

$\sqrt{\frac{25}{64}\cdot \frac{81}{100}}=\sqrt{\frac{25}{64}}\cdot \sqrt{\frac{81}{100}}=\frac{\sout{5}{}^1}{8}\cdot \frac{9}{\sout{10}{}_2}=\frac{8}{18}=\frac{4}{9}$  

 

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b) 

$\sqrt[3]{27\cdot 216}=\sqrt[3]{27}\cdot \sqrt[3]{216}=3\cdot 6=18$  

 

$\sqrt[3]{64\cdot 125\cdot 343}=\sqrt[3]{64}\cdot \sqrt[3]{125}\cdot \sqrt[3]{343}=4\cdot 5\cdot 7=20\cdot 7=140$  

 

$\sqrt[3]{-0,125\cdot \left(-0,027\right)}=\sqrt[3]{-0,125}\cdot \sqrt[3]{-0,027}=-0,5\cdot \left(-0,3\right)=0,15$