\[\boxed{\mathbf{4.}\mathbf{115}}\]
\[1)\ 0,2\ :x = 0,7\ :0,105\]
\[0,7x = 0,2 \cdot 0,105\]
\[x = 0,021\ :0,7\]
\[x = 0,21\ :7\]
\[x = 0,03.\]
\[2)\ \frac{0,6}{0,7} = \frac{x}{3,5}\]
\[x = \frac{3,5 \cdot 0,6}{0,7}\]
\[x = 5 \cdot 0,6\]
\[x = 3.\]
\[3)\ 6,8\ :0,5 = x\ :0,3\]
\[0,5x = 6,8 \cdot 0,3\]
\[0,5x = 2,04\]
\[x = 2,04\ :0,5 = 20,4\ :5\]
\[x = 4,08.\]
\[4)\ \frac{11,7}{6,3} = \frac{14,3}{x}\]
\[x = \frac{14,3 \cdot 6,3}{11,7} = \frac{14,3 \cdot 7}{13}\]
\[x = 1,1 \cdot 7\]
\[x = 7,7.\]