Let f(x)=6x(x3)\displaystyle {f{{\left({x}\right)}}}=-{6}{x}{\left({x}-{3}\right)}.
Then f(4)=\displaystyle {f}'{\left({4}\right)}=   .
And after simplifying f(x)=\displaystyle {f}'{\left({x}\right)}=   .
Hint: You may want to expand and simplify the expression for f(x)\displaystyle {f{{\left({x}\right)}}} first.