Answer:
Total book in the book case=42 books
Explanation:
Bottom three shelves
First shelf= one book taken
Second shelf=two books taken
Third shelf=3 books taken
Total books taken=1+2+3
=6 books
All taken books are placed on the top fourth shelf
Top fourth shelf=6 books
The quantity of books on all the shelves became equal when 6 books are placed on the top fourth shelf.
This means, there are 6 books in each shelf
Total shelves=bottom 3 shelves+ top 4 shelves
=3+4
=7 shelves
The book case has 7 shelves in total.
Each book shelf has 6 books
Total books in the book case=7 shelves × 6 books
=42 books