Answer:33
Step-by-step explanation
The number of books increases by 2,when going from the first to the second shelf. i.e. 3+2=5
Then,when going from the second to the third shelf the number of books increses by 4. i.e. 5+4=9
From the third to the forth shelf the books increase by 6. i.e. 9+6 =15
From the forth to the fifth books increase by 8. i.e. 15+8=23
Therefore from the fifth to the sixth shelf the number of books will increase by 10. i.e. 23+10= 33
