From which story of the building did Eutychus fall when he fell asleep during Paul's sermon?

Answer: The third story

Sinking into a deep sleep in the window, Eutychus fell from the third story (KJV: third loft) and was picked up dead.

“And a certain young man named Eutychus, seated in the window, was sinking into a deep sleep as Paul talked on and on. When he was sound asleep, he fell from the third story and was picked up dead.”— Acts 20:9 (BSB)