Ответ:

1) \(6^{-2}+\left(\frac{3}{4}\right)^{-1}=\frac{1}{6^2}+\frac{4}{3}=\frac{1}{36}+\frac{48}{36}=\frac{49}{36}\).

2) \(\left(\frac{3}{8}\right)^{-1}+3^{-2}-(-46)^0=\frac{8}{3}+\frac{1}{9}-1=\frac{24+1-9}{9}=\frac{16}{9}\).

3) \((8^{-4}\cdot 8^{-9}):8^{-12}=8^{-4-9-(-12)}=8^{-1}=\frac{1}{8}\).

4) \((5^{-2}\cdot5^7):(5^{-5}\cdot5^4)=5^{(-2+7)-(-5+4)}=5^{5-(-1)}=5^6=15625\).

Ответ: 1) \(\frac{49}{36}\); 2) \(\frac{16}{9}\); 3) \(\frac{1}{8}\); 4) \(15625\).