f '(x)= (x+4)^3(2)-(2x)(3)(x+4)(1)
-------------------------
((x+4)^3)^2)
Not sure what to do next. I know I can cancel out something. Can someone assist me?
Presumably you have used the quotient rule to find the derivative here. This just goes to show the futility of teaching the quotient rule (futile as such derivative can be found just as if not more easily using the product and chain rule).