[tex]f(x)=-6x+2\to y=-6x+2\\\\\text{Interchange the y and the x}\\\\x=-6y+2\\\\\text{Solve for y}\\\\-6y+2=x\qquad|-2\\\\-6y=x-2\qquad|:(-6)\\\\y=\dfrac{x-2}{-6}\\\\y=\dfrac{2-x}{6}\\\\Answer:\ f^{-1}(x)=\dfrac{2-x}{6}[/tex]
