who vs. whom

1. (Who/Whom) did you go to the game with?

2. She’s the student (who/whom) writes the best articles.

3. (Who/Whom) did you vote for?

4. (Who/Whom) failed the quiz?

5. We know (who/whom) pulled that prank.

6. We want to know on (who/whom) the prank was pulled.