Since most of them have gone for the rote approach, I'll take an intuitive, slightly different approach. The idea of deviations.
For the remaining 6 days per day she reads 115 pages (690/6)
Now this 115 is 25 greater than 90
Which means she is having to read 25*6 = 150 pages more than usual. Why? Because she slacked by reading only 75 pages instead of 90 pages!
Now if you notice,
150 = 15x (This extra 150 is due to the deviation of reading 15 pages less multiplied by no.of such days)
x = 10
Thus total days = 10+6 = 16.
Answer:
Option Bnelz007
In order to complete a reading assignment on time, Terry planned to read 90 pages per day. However, she read only 75 pages per day at first, leaving 690 pages to be read during the last 6 days before the assignment was to be completed. How many days in all did Terry have to complete the assignment on time?
(A) 15
(B) 16
(C) 25
(D) 40
(E) 46