Here's the instructions:

In Exercises 37-39, use Newton's Law of Cooling, which states that the rate of change in the temperature T of an object is proportional to the difference between the temperature T of the object and the temperature T0 of the surrounding environment. This is described by the differential equation

In the solutions manual they alter the DE to

How do they change it like that? The section it's in is separation of variables so I've been getting all the x's on one side, all the y's on one side, etc. but I don't quite see how they do that at all in this instance...