Determine the inflection points and intervals of concavity for the function $y=3x-\sin x$, where $-\pi \le x\le \pi$.

Inflection point: $x=0$

Concave down on $(-\pi ,0)$

Concave up on $(0,\pi )$

Inflection point: $x=0$

Concave down on $(0,\pi )$

Concave up on $(-\pi ,0)$

Inflection point: $x=\pi$

Concave down on $(0,\pi )$

Concave up on $(-\pi ,0)$

Inflection point: $x=-\pi$

Concave down on $(-\pi ,0)$

Concave up on $(0,\pi )$