Simplify the following expressions involving negative exponents:

1. $4 x^0 y^{-2}=$
   
2. $6^{-2} x^3 y^{-2}=$
   
3. $\frac{2 x^{-4} y^{-3}}{z^{-2}}=$
   
4. $\frac{2 x^0 y^4}{4 y^{-3}}=$
   
5. $\frac{12 a^5 b^{-4} c^6}{36 a^8 b^2 c^4}$