Hl!. I have problems with exercice

Let $\displaystyle I$ and $\displaystyle J$ be ideals in a commutative ring $\displaystyle R$ . Prove that their union $\displaystyle I \cup{J}$ is a ideal if and only if $\displaystyle I\subseteq{J}$ or $\displaystyle J\subseteq{I}$

Hint please

Thanks