[Modules] Show that $h_3$ is injective given comutative diagram

Let $R$ be a ring with $1$. Consider the comutative diagram of $R-modules$ with exact lines attached.
Show that if $h_2$ and $h_4$ are injective and $h_1$ is surjective, then $h_3$ is injective.

Answers can be viewed only if
1. The questioner was satisfied and accepted the answer, or
2. The answer was disputed, but the judge evaluated it as 100% correct.