Which of the following functions is a one$-$to$-$one function?

Question $2$ options:

f: $->,$ where f$($n$)=|$n$|-7$

f: $->,$ where f$($n$)=|2$n $-1|$

f: $->,$ where f$($x$)=2$x $+7$

f: $->,$ where f$($x$)=3$x$^2+6$