Looks like you have most of the details already, but you're missing one crucial piece.
is parameterized by

for
and
, and a normal vector to this surface is

with norm

So the integral of
is

If there are 7 books on the floor, 7 x 3 is 21. Plus two extra books, 21 + 2 = 23. There are 23 books on the bookshelf.
The answer is 2 3/4 or 2.75
Answer:
B
Step-by-step explanation: