Then it's pretty clear what's du and what's u. u, which we set to be equal to x to the fourth plus 7, and then du is equal to this. It's equal to 4x to the third dx. We saw it right over here. So we can rewrite this integral, and I'll try to stay consistent with the colors, as the indefinite integral. What we have in magenta right over here, that's du over x to the fourth plus 7, which is just u. Or we could rewrite this entire thing as the integral of 1 over u du. What is the indefinite integral of 1 over u du?