Simplify

i got the answer again but im not sure about the bottom half since i just cube rooted the 81 and wasnt sure what to do with the 4 part of it.... dont know if this is coincidently the right answer that i got...

please explain the method, thanks!

sorry i cant get the hang of the [tex] thing , its suppose to be 16^half all over (divided by) 81^three quarters