Correct Answer - Option 1 : 14
Naman remembers his friend's marriage is after 13th May (i.e. on 14th, 15th, 16th, etc.) while his sister remembers the date is before 15th May (i.e. on 14th, 13th, 12th, etc.).
Combining both the statements we get only one possible date which is 14th May.
Hence, option (1) is the correct answer.