90 pages are 1 of the whole book, indicating that the whole book has

90 divided by two 1 (that is, 90*2)

It is concluded that the book has 180 pages.

Read five more pages a day, which means reading 10+5= 15 pages a day.

I have read 90 pages, 180-90=90 pages, and I still have 90 pages left.

90 divided by 15=6 (days)

A: It takes six days to read it.