Here's one approach . . .
You read 8 plays over 2 days, 4 plays per day.
If Hamlet and Macbeth are two of the plays,
what is the probability that you read them on the same day?
There are: ways to read the books.
There are two cases to consider:
If you read Hamlet and Macbeth on the first day,
. . there are choices for the other 2 books read the first day.
. . The other 4 books are read the second day.
If you read Hamlet and Macbeth on the second day,
. . there are choices for the other 2 books read the second day.
. . The other 4 books are read the first day.
Hence, there are ways that Hamlet and Macbeth can be read on the same day.