Ответ:

  1. \(-2x+3x-4x=-3x\).
  2. \(0.2x-4x-\frac15y=-3.8x-0.2y\).
  3. \(\frac29x-2x+\frac79y=-\frac{16}{9}x+\frac79y\).
  4. \(3x-\frac25x-0.6x=2x\).
  5. \(\frac12x+x+\frac12x-x=x\).
  6. \(-\frac45x-0.2x-x=-2x\).