"You finished writing the letter."
Translation:Usted terminó de escribir la carta.
Some verbs require a preposition before an infinitive. Terminar de + infinitive = to stop doing something or to finish doing something
An accent is needed over the "o" for it to be past tense. Terminó.
Termino de escribir la carta = I finish writing the letter
Terminó de escribir la carta = You finished writing the letter.
Terminaste de escribir la carta = You finished writing the letter.
I just typed "Terminaste escribir la carta" and it wasn't accepted. I understand from the other comments that you need a "de" involved, and that tú form is now accepted, but my error message was still this:
You used the tú form "terminaste" instead of the él/ella/usted form "terminó".
Please fix the error message because I was very confused.
The message is confused. It is the lack of "de" that is the problem.
"Terminaste" is unacceptable for some reason, although there is no context to suggest Usted is the only acceptable answer