I came across two functions I am having trouble with and I am not really sure why.

the function is f(t)= 64t/(8+t)^3

I tried the quotient rule which then translates into

64[(1)((8+t)^-3)-3t(8+t)^-4]/[(8+t)^3]^2

from there it goes to crap, the answer that it should be is 128(4-t)/(8+t)^4 which is not the answer I end up with. thank you.