B) x + 6 = 2x - 15; 4 7 г) 0,3 x+5 0,8 x-9

в)

\[\frac{x+6}{4} = \frac{2x-15}{7}\]

\[7(x+6) = 4(2x-15)\]

\[7x + 42 = 8x - 60\]

\[7x - 8x = -60 - 42\]

\[-x = -102\]

\[x = 102\]

Ответ: x = 102

г)

\[\frac{0.3}{x+5} = \frac{0.8}{x-9}\]

\[0.3(x-9) = 0.8(x+5)\]

\[0.3x - 2.7 = 0.8x + 4\]

\[0.3x - 0.8x = 4 + 2.7\]

\[-0.5x = 6.7\]

\[x = \frac{6.7}{-0.5}\]

\[x = -13.4\]

Ответ: x = -13.4