Let's assume that the student has already completed three semesters and has received a total of "x" marks out of a maximum possible of 300 (i.e., the total marks of three semesters).
To achieve a distinction (75%), the student needs to obtain at least 75% of the total possible marks in all four semesters. That means she needs to secure a minimum of 75% of 400 (i.e., the total marks of all four semesters) which is equal to 300 marks.
Since the student has already obtained "x" marks in the previous three semesters, she needs to obtain a minimum of 300 - x marks in the fourth semester to secure a distinction.
For example, if the student has obtained 200 marks out of 300 in the previous three semesters, she needs to obtain a minimum of 100 marks (300 - 200) in the fourth semester to achieve a distinction.
So, the number of marks that the student needs to obtain in the fourth semester to secure a distinction depends on the total marks she has obtained in the previous three semesters.