Ответ:

  1. \(-9a+5y-3y-6a=-15a+2y\).
  2. \(10a-15d+11c-12a-25d=-2a+11c-40d\).
  3. \(-8-c+3a-6c+3-a=2a-7c-5\).
  4. \(5.3a-4c+1.8a+5-3c=7.1a-7c+5\).