Jo reads at a steady pace. Her current book has 210 pages. Now, she is at page 90. An hour ago, she was at page 60. For how many hours will she be reading the book?
She reads 90-60=<<90-60=30>>30 pages in an hour.
She needs to read 210-90=<<210-90=120>>120 more pages.
For an additional 120 pages, she will need 120/30=<<120/30=4>>4 hours.
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