You answered everything correctly.
First one isn't answer because 3^x is exponetial while x^3 is cubic function. If you draw them you will see that they are very different.
B is correct because we can divide both numerator and denominator by 6 and we get 3^x
C is not correct because x is not powering 3 so we cannot devide both by 6
D is correct because 3^(x-1) is same as 3^x*3^(-1) = 3^x/3 and when multiplied by 3 we get 3^x
E is not correct. will understand after explanation in D
F is correct. x is powering both numbers so it can be outside parethasis.
