3 hours is equivalent to 180 minutes.
The amount of remaining time is 150 minutes.
Since there are still 30 remaining papers left, therefore:
Time allotted per paper = 150minutes/30papers = 5 minute per paper
The time allotted for the 5 finished papers is:
Time allotted before = 30minutes/5papers = 6 minutes per paper
Therefore she must work 1 minute per paper faster.