A certain novel is available in hardcover and paperback. lf the store

We know from the question stem that H + P = 100 .................(1)
where H is the number of hardcover novels, and P is the number of paperback novels.
We are to determine the number of paperback novels available out of the total stock of 100 novels.

Statement 1:
If twenty hardcover versions are sold, there would be three times as many hardcover versions left as paperback versions.
Statement 1 is sufficient. This is because we are able to determine that out of the 80 novels left in stock after selling 20 hardcover versions, the ration of H:P=3:1; hence we can calculate the number of paperback versions left in stock to be 20. In addition, since the 20 previously sold were hardcover, then it means the total paperback that was in stock is also 20.

Statement 2: says that if a hardcover version costs twice as much as a paperback version, the total sales of all the books in stock will be $90.
Statement 2 is not sufficient.
Assuming that a paperback version costs $0.5, then a hardcover costs $1.
from (1) we can say H=100-P
100-P + 0.5P = 90
P=20.

however if a paperback costs $0.6 then a hardcover costs $1.2
1.2(100-P)+0.6P = 90
120P -1.2P +0.6P =90
0.6P=30
P=50.

We can conclude that Statement 1 alone is sufficient. The answer has to be therefore A in my view.