Sophia finished 2 3 of a book she calculated that she finished 90 more pages than she has yet to read How long is her book?

If Sophia finished 2/3 of the book and has 90 more pages left to read than she has already read, then the total number of pages in the book is 3/3 or the whole book. 2/3 of the book equals the number of pages she has read, so 1/3 of the book equals 90 pages. Therefore, the total length of her book is 3 * 90 = 270 pages.