$3)$ Consider the Bank database of Figure $2.$ What is the appropriate primary key for each relation?

$4)$ Consider the Bank database of Figure $2.$ Give a relational algebra expression to perform each of the following queries:

$-$ Find the name of each branch located in $$Houston$.$

$-$ Find the ID of each borrower who has a loan in branch $$Downtown$$

$-$ Find the name of each borrower who has a loan in branch $$Downtown$$