Possessive Adjective Q's

Question

I am studying for my Spanish final and I have a few quick questions regarding possessive adjectives.

Choose the possessive adjective that can be modified to match gender AND number.

-mis

-vuestro

-mi

-su

Choose the possessive adjective that can also be used formally with usted.

-tu

-nuestro

-su

-mi

Thanks in advance for your help!

Answer 1

Vuestro can match gender and number (vuestro, vuestra, vuestros and vuestras), All the others can match only gender or number or none of them. I'd say that in the second question correct answer is "su", because it refers to the third person, singular. But, if you want to say that something belongs e.g. to you and Mr. Smith, you can also say that this thing is "nuestro". I thing it's the only way to say "our" in Spanish.