Help me understanding this Exercise Question
I'm not really sure this is truly a DBA question, as it sounds like your problem is understanding the question itself.

The question asks which books generate less than 55% profit. Profit would be the difference between retail and cost. So, the question is, what should the profit be less than 55% of? The basic options are 55% of retail, or 55% of cost. I would assume that retail is intended.

So, you'd need to calculate which books show retail - cost as less than 55% of retail. Then, make a call as to what "recently" means (given orders from just two months, I'd go for all of those orders), and sum the total quantities ordered for each of those books.