First, subtract the number of days Jenna can't read from the number of days in September: 30 days - 4 days = <<30-4=26>>26 days.
Then subtract the one day when Jenna will read 100 pages: 26 days - 1 day = <<26-1=25>>25 days.
Now subtract the 100 pages Jenna will read on her flight from her overall goal: 600 pages - 100 pages = <<600-100=500>>500 pages.
Finally, divide that number of pages by the number of days Jenna will read the standard amount: 500 pages / 25 days = <<500/25=20>>20 pages per day.
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