Answer:
The number of copies sold is  statistically difficult to determine.
Explanation:
The determination of the number of books sold by a particular author is a difficult task going by the fact that, most of the sale are made online and at various stores. Most of the customers that bought the books hardly leave feedback which would have aided in compiling the total number.
Also, some are sold as hard copies at various stores available within the author's country of residence and outside of it.
In summary, while looking at the Amazon website, I am optimistic that the author, Artwoodwrite was able to sell a substantial amount of the book Brain friction (Wondering of the mind).
