Initially Terry was planning to read 90 pages/ day. But, she only reads 75 pages / day for few days and in the final 6 days, she needs to read 690 pages.
Thus, if we give her 16 days,
90*16 = 1440 pages and 690 + 75(16-6) = 690 + 750 = 1440.
Thus, option B.

Let's start with a word equation

We can write: (total number of pages to be read at INTENDED rate of 90 pages/day) = (total number of pages ACTUALLY read at 75 pages/day) + 690 more pages

Let x = number of days to complete reading assignment at 90 pages per day
So, x - 6 = number of days reading at 75 pages per day (since Terry spent the last 6 days reading 690 pages)

At a rate of 90 pages/day, 90x = number of pages that COULD be read in x days
At a rate of 75 pages/day, 75(x - 6) = number of pages ACTUALLY read in x-6 days

We get: 90x = 75(x - 6) + 690
Expand to get: 90x = 75x - 450 + 690
Simplify to get: 90x = 75x + 240
We get: 15x = 240
Solve: x = 240/15 = 16

Answer: B

Cheers,
Brent

with x = number of days

with her initial plan, we conclude the book number of pages is 90x
with the revised plan, the book number of pages is 75(x-6) + 690

90x = 75(x-6) + 690

90x = 75 - 450 + 690

x = 16

Answer B

I am not getting the point!

90pg/1day but spent 75pg/day with a remaining 690 pgs on the last 6 days.

We know she would have finished the book on time if she had read 90 pages per day but at this lower rate she won't be able to finish it on time. How many pages short will she be?

690 - 75*6 = 690 - 225*2 = 690 - 450 = 240 pages short.

We know she would have finished had she been reading 90 pages each day. The difference between these rates in 15pg a day. Since she fell behind 15 pages every day, 240/15 should give us the correct answer. (8*3*5*2)/(3*5) = 8*2 = 16

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