When we are using the subfiles package you can use one simple command to "tell" each chapter to use the preamble from the main document. Start each chapter file with the following command: \documentclass[../main.tex]{subfiles}. Then you can start your document using the \begin{document} command, for example like this:

preamble chapter.JPG

When you are working in this chapter you can compile it by itself, that is usually a bit quicker than compiling the entire document and it gives you a better overview of your content. You can add all kinds of content to this file in the exact same way as you would add it in the main document.

Task

Add the command that makes the chapter files use the preamble from the main document to all your chapters. 1) Compile each chapter and make sure that they work seperately before you 2) compile the main document and check that it works as a whole.