the book wants you to evaluate the indefinite integral, .
There may be a few ways to deal with this. We can expand (5x-4)^4 using binomial theorem, then integrate it term by term. But this is long, tiring and unnecessary, so we won't use this approach.
If we can reduce 5x-4 to one term, we can integrate it easily.
Substitute and it's easy to finish from there.