Find f '(x) for the functions

1.) f(x) =x34x+86x8

2.) f(x) =38ex1

3.) f(x) = 3x⁴e^x

4.) Find all values of x (if any) where the tangent line to the graph of the given equation is horizontal. HINT [The tangent line is horizontal when its slope is zero.] (Enter your answers as a comma-separated list. If an answer does not exist, enter DNE.)

y = x +x1