ПОМОГИТЕ ПОЖАЛУЙСТА!Нужна помощь с 3 и 5.

Решите задачу:

$\sqrt{21} - \sqrt{22-2 \sqrt{21} } = \sqrt{21} - \sqrt{1-2 \sqrt{21}+(\sqrt{21})^2 } = \\\ = \sqrt{21} - \sqrt{(1- \sqrt{21})^2 } = \sqrt{21} - |1- \sqrt{21}|= \sqrt{21} +1-\sqrt{21}=1$

$(0.(6)^3- \sqrt{0.(4)} )^{-1}=( (\frac{2}{3})^3- \sqrt{ \frac{4}{9} } )^{-1}= (\frac{8}{27}- \frac{2}{3} )^{-1}= \\\ =(\frac{8}{27}- \frac{18}{27} )^{-1}=(- \frac{10}{27} )^{-1}=-2.7$