\[\boxed{\mathbf{6.7}}\]
\[\textbf{а)}\ 3a - 4 = 2a + 6\]
\[3a - 2a = 6 + 4\]
\[a = 10.\]
\[\textbf{б)}\ \frac{4}{7}x + \frac{3}{7} = \frac{1}{7}x\]
\[\frac{4}{7}x - \frac{1}{7}x = - \frac{3}{7}\]
\[\frac{3}{7}x = - \frac{3}{7}\]
\[x = - 1.\]
\[\textbf{в)}\ 1,7y - 1 = 1,3y + 1,4\]
\[1,7y - 1,3y = 1,4 + 1\]
\[0,4y = 2,4\]
\[y = 2,4\ :0,4 = 24\ :4\]
\[y = 6.\]
\[\textbf{г)}\ \frac{4^{\backslash 3}}{7}x = \frac{4}{21}x - \frac{8}{21}\ \]
\[\frac{12}{21}x - \frac{4}{21}x = - \frac{8}{21}\]
\[\frac{8}{21}x = - \frac{8}{21}\]
\[x = - 1.\]