Ответ:

  1. \((6^4)^4:(6^5)^3=6^{16-15}=6\).
  2. \(8^3:4^4=2^9:2^8=2\).
  3. \(7^{14+6-18-2}=1\).
  4. \(5^{6+6-10}=5^2=25\).
  5. \(21^8:21^7=21\).
  6. \((5^9\cdot 2^{12})/(2^{12}\cdot5^6)=5^3=125\).