To find the passing marks, we need to understand the given information and solve the problem step by step. Let's break it down:

Given Information:
- The student required 40% marks to pass the exam.
- The student scored 35%.
- The student failed by 15 marks.

Step 1: Determine the Total Marks
To find the passing marks, we first need to determine the total marks for the exam. We can set up an equation using the given information.

Let's assume the total marks for the exam as "x".

Step 2: Calculate the Passing Marks
According to the given information, the student required 40% marks to pass the exam. So, we can write the equation as:

40% of x = Passing Marks

To calculate 40% of x, we can multiply x by 0.40:

0.40x = Passing Marks

Step 3: Calculate the Scored Marks
According to the given information, the student scored 35% marks. So, we can calculate the scored marks by multiplying the total marks (x) by 0.35:

0.35x = Scored Marks

Step 4: Calculate the Difference
The student failed by 15 marks, which means the scored marks were 15 less than the passing marks. We can set up an equation using this information:

Passing Marks - Scored Marks = 15

Substituting the values from Step 2 and Step 3:

0.40x - 0.35x = 15

Simplifying the equation:

0.05x = 15

Dividing both sides by 0.05:

x = 15 / 0.05

x = 300

Step 5: Find the Passing Marks
Now that we have determined the total marks (x), we can calculate the passing marks by substituting the value of x into the equation from Step 2:

0.40 * 300 = 120

Therefore, the passing marks for the exam are 120.

The correct answer is option D) 120.