You have one over w minus 300, dw, let me make sure that the dw doesn't look like it's in the denominator, dw, is equal to one over 25 dt. And now, we can integrate both sides, which is essentially just saying that we're taking, since this is equal to this, that each little increment of w times this is equal to each little increment of dt times one over 25. We can then say, well, if we sum up all of the increments of w times this quantity, if we sum up the infinite number of infinitesimally small increments, that would be the same thing as summing up all of these characters, because each of these characters is really the same as each of these characters. So, let's do that sum. We're essentially just taking, we're just integrating both sides of this. And here, you might be able to do this in your head, or we could do the formal u substitution, just to make it clear what we're doing. If you said u is equal to w minus 300, then what is du?