The answer to the first question is as follows: 4 days 1/3, that is, (500x 1/3)/4 per day.
Days required for completion: the remaining unfinished part/the speed of completion every day.
That is: (500x2/3)/[(500x1/3)/4] = 8 days.
So it takes eight days to finish a week.
The answer to the second question is as follows.
Suppose this book has x pages, and we have read 1/8X+ 12 pages.
What I haven't seen is page X -( 1/8X+ 12).
[ 1/8X+ 12]/[X-( 1/8X+ 12)]= 1/4
Solve X= 160
This book is on page *** 160. I hope you can make progress in your study.