Ответ:

  1. \(80 \cdot 8 + 60 = 640 + 60 = 700\);
  2. \(7 \cdot 70 - 90 = 490 - 90 = 400\);
  3. \(4 \cdot 60 - 40 = 240 - 40 = 200\);
  4. \(50 \cdot 5 + 50 = 250 + 50 = 300\);
  5. \(30 \cdot 3 + 10 = 90 + 10 = 100\);
  6. \(9 \cdot 90 - 10 = 810 - 10 = 800\).