Is cubic function a one-one function?

Using the functions $f$ and $g$ given below, find $f\circ g$ and $g\circ f$. Check whether $f\circ g=g\circ f$

$f\left(x\right)=x-6, g\left(x\right)=x^2$

Using the functions $f$ and $g$ given below, find $f\circ g$ and $g\circ f$. Check whether $f\circ g=g\circ f$

$f\left(x\right)=\frac{2}{x}, g\left(x\right)=2x^2-1$

Using the functions $f$ and $g$ given below, find $f\circ g$ and $g\circ f$. Check whether $f\circ g=g\circ f$

$f\left(x\right)=\frac{x+6}{3}, g\left(x\right)=3-x$

Using the functions $f$ and $g$ given below, find $f\circ g$ and $g\circ f$. Check whether $f\circ g=g\circ f$

$f\left(x\right)=3+x, g\left(x\right)=x-4$

Using the functions $f$ and $g$ given below, find $fog$ and $gof.$ Check whether $f\circ g=g\circ f$

$f\left(x\right)=4x^2-1, g\left(x\right)=1+x$

Find the value of $k,$ such that $f\circ g=g\circ f$

$f\left(x\right)=3x+2, g\left(x\right)=6x-k$