Answer:
[tex]\sqrt[3]{\dfrac{6-x}{4}}[/tex]
Step-by-step explanation:
[tex]f(x)=6-4x^3\implies y=6-4x^3\implies y-6=-4x^3\implies \sqrt[3]{\dfrac{6-y}{4}}=x\implies\\\implies f^{-1}(x)=\sqrt[3]{\dfrac{6-x}{4}}[/tex]