Final answer:
The pronoun 'usted' is used to talk to your friend's grandmother in Spanish.
Step-by-step explanation:
To talk to your friend's grandmother in Spanish, you would use the pronoun usted. In Spanish, usted is the formal way to address someone older or in a position of authority, such as a friend's grandmother. It is used to show respect and politeness. For example, you could say 'Hola, ¿cómo está usted?'
Learn more about Pronoun usage in Spanish