Determine the intervals on which the function $h$ is increasing or decreasing, given its derivative $h^{\prime }\left(x\right)=(x+15)(x+21)(x-13)$.

Increasing on: $(-\infty,-21)\cup(-13,15)$

Decreasing on: $(-21,-13)\cup(15,\infty)$

Increasing on: $(-21,-13)\cup (15,\infty )$

Decreasing on: $(-\infty ,-21)\cup (-13,15)$

Increasing on: $(-\infty,-21)\cup(-15,13)$$(-21,-15)\cup(13,\infty)$

Decreasing on: $(-21,-15)\cup(13,\infty)$$(-\infty,-21)\cup(-15,13)$

Increasing on: $(-21,-15)\cup(13,\infty)$

Decreasing on: $(-\infty,-21)\cup(-15,13)$