B) x=x+x+0,8x-xx-x;

в) $$x \cdot \frac{2}{3}x + \frac{1}{4}x + 0,8x - x \cdot x - \frac{1}{6}x = \frac{2}{3}x^2 + \frac{1}{4}x + 0,8x - x^2 - \frac{1}{6}x = \frac{2}{3}x^2 - x^2 + \frac{1}{4}x + 0,8x - \frac{1}{6}x = -\frac{1}{3}x^2 + \frac{3}{10}x + \frac{4}{5}x = -\frac{1}{3}x^2 + \frac{3}{10}x + \frac{8}{10}x = -\frac{1}{3}x^2 + \frac{11}{10}x$$.

Ответ: $$\frac{-1}{3}x^2 + \frac{11}{10}x$$