question of passive voice

[Lie.K.]

Hello

When I'd like to ask about the agent of passive voice, can I use both sentences?
Or is "By whom " not used in daily life?

For example:
1) By whom was the cake eaten?
2 Who was the cake eaten by?

Thank you. :)

[Alan]

While constructions such as 'who...by' are widely accepted, 'by whom' is still considered correct for formal use.