Explanation:

- The average marks of all 180 students is 50.

- Let the number of students who passed be \( x \) and the number who failed be \( y \).

- Passed students' average is 80, so their total marks are \( 80x \).

- Failed students' average is 40, so their total marks are \( 40y \).

- We know \( x + y = 180 \).

- Average of overall students is 50, so total marks are \( 180 \times 50 = 9000 \).

- Total marks equation: \( 80x + 40y = 9000 \).

- Substitute \( y = 180 - x \) into total marks equation:

- \( 80x + 40(180 - x) = 9000 \)

- \( 80x + 7200 - 40x = 9000 \)

- \( 40x = 1800 \)

- \( x = 45 \)

- \( y = 180 - 45 = 135 \)

? Option 2: 135 is the correct answer.

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