Answer:
Bruh, this is honestly beautiful!
Explanation:
The correct answer is <em>who.
</em>The teacher knew it was Sam who was passing notes.
It would be <em>whom </em>in this case:
The teacher knew it was Sam <em>whom </em>they were passing notes to.
Not to be rude, but this question shouldn't be in the English section because it's a word problem. Please post in the mathematics section. :) Good luck!!!