Hello/Hola, Aliwitt
Question/Pregunta : ¿Cuál palabra está escrita correctamente?
Answer/Respuesta : interés
Why/Porque : interés would be the answer because interes is another word.
interés means the value of something while interes means interesting or that your interested in something. Mainly you put a comma on top of the letter to change the meaning.
-procklown