Problem:

So I am kind of stumped with these Us in the equation. Our professor has been gracious enough to point us to an integral solving site, but I get different answers based on switching U for X.

I don't think I need to switch any of the variables out, but I am trying to figure out where I want to go from here. It doesn't seem like I should use the substitution method on this, but I could be wrong. Could someone walk me through this?