Question

4. Vamos a
casa. (their)
a.
Su
b. Tu
c. mi​

Answer 1

The answer would be su.

Vamos a su casa.

Tu makes the most sense, and it is referring to the other person, in the conversation. The english translation of "Vamos a su casa." is "Let's go to your house." So su is the best answer

Hope this helps

ヽ(*・ω・)ﾉ

Answer 2

A. Su

Step-by-step explanation:

Because Su literally translates to their. Tu means you/your and mi means mine/my.

If it were casas, then you just modify the pronoun to sus.