Salvador wants to evaluate $81^{3/4}$. He knows that $3^4=81$, so he substitutes and uses the power property for exponents: $81^{3/4}=(3^4)^{3/4}=3^3=27$. Use Salvador’s technique to evaluate each of the following expressions. 

1. $81^{-3/4}$ 

   Step (a):

   $\frac{1}{81^{3/4}}$ 

2. $27^{2/3}$ 

   Step (b):

   $( 3 ^ { 3 } ) ^ { 2 / 3 } = 3 ^ { 2 } = ?$ 

3. $\left(\frac{125}{64}\right)^{2/3}$ 

   Step (c):

   $( ( \frac { 5 } { 4 } ) ^ { 3 } ) ^ { 2 / 3 }$ 

4. $\left(\frac{1}{9}\right)^{-1/2}$ 
   

   Step (d):

   $9^{1/2}$