"You arrived at the institute."
Translation:Usted llegó al instituto.
The verb's conjugation is different: "Usted llegó al instituto" and "Tú llegaste al instituto" are both accepted.
Why do we use en su casa, but al instituto, at your house, at the institute? En versus a?
Yes i agree that "tu" should be accepted but i do know that the difference between "usted" and "tu" "Usted" is used formally like you would use that with a stranger and "tu" is used for people you know in your everyday life so maybe this sentence represents someone who is speaking formally maybe somebody should report this question tough
Again, the english doesn't denote familiar or formal, plural or singular, so all those responses should be accepted.