Answer:
129 pages.
Explanation:
Let's call
the total number of pages.
He reads
on Monday. There are 13/15 left.
on Tuesday. There are 2/3 left.
on Wednesday. There are 7/9 left.
Now, the remainder would be the difference between
and all pages read at this point

So, 3/4 of this is

The sum of all pages read is

Therefore, there are around 129 pages.