Good morning.
"Synthesizing" is a word that means nothing more than "interpreting" or "understanding." It sounds like the assignment wants you to look at these works from these different authors and understand how they use motivation in the work.
You can start by making a list. What kinds of motivation are used in each of the texts? Once you have identified those theories you can then analyze them individually, or compare a couple of them together.
I hope this helps you get started. Once you have a list, I can help you organize your paper.
Regards,
Gloria
Moderator, EssayForum.com
Gloria, EssayForum.com