The thread title betrays some misunderstanding: "Convert to a first order ODE".The question is asking you to solve it in a particular way. It Ii almost telling you the way when it says ' convert to first-order o.d.e.'.
I agree. Your first resource should be your textbook, which almost certainly has an example of a problem like this.Helpers are not here to re-write the textbooks but to help out with difficulties or confusions in understanding points or difficulties students run into trying to apply the methods.