I track my time for everything I write. That is the only way I know how to quote projects. If you don’t have that data, give it your best guess and add 10-20% for unforeseen things. Also, for the future, you will almost always make more money charging by the project. When you work by the hour, you’re penalized for being a fast writer. Think of it as charging for the value you bring to the table, not the time it took to do it.