When will I get my libarary book???

I can't do the math, but I can offer you an English tip: "simplistic" doesn't mean the same as "simple". The adjective simple means plain, easy, ordinary, or uncomplicated. A simple solution to a problem is usually a good solution. In addition, simple is sometimes used as a synonym for naive or unsophisticated.

The adjective simplistic is a pejorative word meaning overly simplified—that is, characterized by extreme and often misleading simplicity.

if 4 weeks is the max, then it's X times 4 for the most basic answer, realisticly there are many variables that could affect the answer

for instance, my local library is part of group of libraries, so if i look up a book online, put it on hold i'm told how many folks are in line ahead of me, what i don't know is, how long has the current holder of the book had it, when it's finally returned, how many days will it take to get to each person ahead of me, if it has to move from one library to another, that may take a day or two, plus once a person gets the notification the book is ready for pickup, they have 3 days (at my library) to pick it up, and only then does the time begin counting down for how long you can have the book