Answer
$$\frac{\tan ^{5} x}{5}+C $$
Work Step by Step
Let $ u= \tan x\ \ \ \Rightarrow \ du=\sec^2xdx $, then
\begin{align*}
\int \tan ^{4} x \sec ^{2} x d x&=\int u ^{4} d u\\
&=\frac{u ^{5} }{5}+C \\
&=\frac{\tan ^{5} x}{5}+C
\end{align*}