1) 

It is the 4th root of 216. Using a calculator, you get the answer as 

I think you may have confused exponentiation (^) with the multiplation (*) operation.

6*3/4 = 4.5, but 6^(3/4) = 3.83.

2) 

=  ---> take the cube root of -125 and square it
= 
=

Hope you got it :)