For your question 3:
As per the statement, Store S sold different number of copies on ANY TWO OF THE DAYS, and also states that Store S sold greatest number of copies on Satrurday and second greatest number on Friday,
so its a clue only on Friday and Saturday, Store S sold different number of copies and rest all 5 days sold the same number of copies.
1. 8 books on thursday
Insufficient: Gives the number of copies sold from Mon - Thu, but what about Friday/Saturday?
2. Sold 38 books on Saturday
Sufficient:
Satrurday: 38
Remaining copies: 52,
As store S sold same number of copies from Mon-Thu, try any number 2,3,4,5,6,7,8 all of these number suggests Store S sold more that 11 copies on Friday.
Hence Answer B.