Step 1: Recall the definition of \(\cosech x\).
We know that
\[
\cosech x=\frac{1}{\sinh x}
\]
Given,
\[
\cosech x=\frac45
\]
Therefore,
\[
\frac{1}{\sinh x}=\frac45
\]
Step 2: Find \(\sinh x\).
Taking reciprocal on both sides,
\[
\sinh x=\frac54
\]
Step 3: Final conclusion.
Hence,
\[
\boxed{\frac54}
\]