Answer:3Step-by-step explanation:We know:[tex]f\bigg(f^{-1}(x)\bigg)=x[/tex]Therefore[tex]f\bigg(f^{-1}(3)\bigg)=3[/tex]Other method.Find [tex]f^{-1}(x)[/tex][tex]f(x)=3x+12\to y=3x+12[/tex]exchange x to y and vice versa:[tex]x=3y+12[/tex]solve for y:[tex]3y+12=x[/tex] subtract 12 from both sides[tex]3y=x-12[/tex] divide both sides by 3[tex]y=\dfrac{x-12}{3}\to f^{-1}(x)=\dfrac{x-12}{3}[/tex][tex]f\bigg(f^{-1}(x)\bigg)[/tex] replace x in f(x) with the expression [tex]\dfrac{x-12}{3}[/tex][tex]f\bigg(f^{-1}(x)\bigg)=3\cdot\dfrac{x-12}{3}+12=x-12+12=x[/tex][tex]f\bigg(f^{-1}(3)\bigg)[/tex] - put x = 3 to [tex]f\bigg(f^{-1}(x)\bigg)[/tex][tex]f\bigg(f^{-1}(3)\bigg)=3[/tex]