\[- 4(3,5x - 4) - (7 - 2,1x) + 5(0,3x - 5) =\]
\[= - 14x + 16 - 7 + 2,1x + 1,5x - 25 =\]
\[= - 10,4x - 16;\]
\[x = - \frac{10}{27}:\]
\[- 10,4 \cdot \left( - \frac{10}{27} \right) - 16 =\]
\[= \frac{104}{10} \cdot \frac{10}{27} - 16 = \frac{104}{27} - 16 =\]
\[= 3\frac{23}{27} - 16 = - 12\frac{4}{27}.\]