Ответ:

  1. \(5.4a+1+8.2a=(5.4a+8.2a)+1=13.6a+1\).
  2. \(7+3.2x-1.8x+1.3=(3.2x-1.8x)+(7+1.3)=1.4x+8.3\).
  3. \(6.32b-0.8b+2.1=(6.32b-0.8b)+2.1=5.52b+2.1\).

Ответ: 13,6a + 1; 1,4x + 8,3; 5,52b + 2,1.