Simplify & write the answer using positive exponents:

1. (3^3)(3^-6)

2. S^2 t^-1 / (s^4 t^4)^1/2
Simplify then evaluate, express answer to 4 decimal places where nessasssary :
3. [(2/3)^2]^-3
4. [(1-4)^-3 Divide (1/4)^2]^-2