4:45 -3:30 -2*(0:15) = 0:45
Gina and Lucy can spend 45 minutes at the library.
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They will get to the library at 3:45. They must start home by 4:30. From 3:45 to 4:00 is 15 minutes, and it is 30 more minutes to 4:30. The time they can spend at the library totals 45 minutes.