Ответ:

  1. \(99 \cdot 6 = (100 - 1) \cdot 6 = 600 - 6 = 594\).
  2. \(959 : 7 = 137\), так как \(137 \cdot 7 = 959\).
  3. \(603 - 427 = 603 - 400 - 27 = 203 - 27 = 176\).
  4. \(856 : 4 = 214\).
  5. \(506 - 139 = 506 - 100 - 39 = 406 - 39 = 367\).
  6. \((30 + 160 : 4) : 2 = (30 + 40) : 2 = 70 : 2 = 35\).
  7. \(280 - 40 : 2 + 100 = 280 - 20 + 100 = 360\).

Ответ: 594; 137; 176; 214; 367; 35; 360.