Explanation:

- Ena is ranked 18th from the top among those who passed the examination.

- She is ranked 39th from the bottom among those who passed.

- This means the total number of students who passed is 18 + 39 - 1 = 56 (since Ena is counted in both ranks).

- Additionally, 10 students did not appear for the examination.

- Moreover, 4 students failed the examination.

- So, the total number of students in the class is the sum of those who passed, those who did not appear, and those who failed: 56 + 10 + 4 = 70.

Hence, the total number of students in the class is 70.

Option 4: 70 is correct.