since you are multiplying and not adding all you have to do is multiply your exponents

(x^(3/4)^8 = 3/4*8=24/4=6 ... x^6

y^1/4 ^8 = 8*1/4=8/4=2 .... y^2

x^6y^2 <----------

is your answer, however, you can only do this with multiplication and division if you are adding you must expand then simplify (x+1)^2 does not equal x^2+1 it is x^2+2x+1