Ответ:

  1. \(85\cdot4=340\).
  2. \(45:3=15\).
  3. \(18\cdot40:60=720:60=12\).
  4. \(450:(70+80)=450:150=3\).
  5. \(20:(12-8)=20:4=5\).
  6. \((70+80)\cdot3=150\cdot3=450\).