There is really one variable in this question: other unknowns can be derived from the number of days in total Terry has to complete the reading assignment. So let x be that number of days. We have:

90x = Total number of pages = 75(x-6) + 690

So 15x = 240

x = 16

QED.

_________________

Are you aiming for a 700+ GMAT score and a top 10 MBA?

If you are, we should talk. I specialize in ambitious students.

$80/hour as of May 2018.

http://www.facebook.com/HanoiGMATtutor

HanoiGMATTutor@gmail.com