Shon got 18% of the total marks which is less than the passing marks by 18. Kirti secured 80% of the total marks which is 75 more than the passing marks. Find the passing marks.

Let's solve this step by step:

1. Let's assume the total marks are 100 (this simplifies calculations and doesn't affect the ratio or percentages).

2. According to the problem, Shon got 18% of the total marks, which is 18 marks. But this is 18 marks less than the passing marks. So, the passing marks = 18 (Shon's marks) + 18 = 36 marks.

3. On the other hand, Kirti secured 80% of the total marks, which is 80 marks. This is 75 marks more than the passing marks. So, the passing marks = 80 (Kirti's marks) - 75 = 5 marks.

4. We have two different values for the passing marks, which is not possible. Therefore, we need to adjust our assumption about the total marks.

5. Let's assume the total marks are 'x'. Then, Shon's marks are 18% of 'x' and Kirti's marks are 80% of 'x'.

6. According to the problem, Shon's marks are 18 less than the passing marks and Kirti's marks are 75 more than the passing marks. So, we can set up the following equations:

   0.18x + 18 = passing marks 0.80x - 75 = passing marks

7. Since both expressions are equal to the passing marks, we can set them equal to each other and solve for 'x':

   0.18x + 18 = 0.80x - 75

8. Solving this equation gives x = 150.

9. Substituting x = 150 into either of the original equations gives the passing marks = 45.

So, the passing marks are 45.