If RI and PK are not provided, then min = 0 (No tuples is common) and max = 1200 (if all tuples are same) [This seems correct according to the question]
If enroll’s roll no is a FK referencing to student’s roll no and roll no is not a PK in any of the table, then min = 40 and max = 1200.
If enroll’s roll no is a FK referencing to student’s roll no and student’s roll no is a PK, then min = 40 and max = 40.
If enroll’s roll no is a FK referencing to student’s roll no and roll no is PK in both the table, then min = 30 and max = 30
If No FK is provided and roll no is PK in both the table, then min = 0 (No tuple is common) and max = 30.
PS : Source – maximum and minimum number of tuples in natural join