Question: Can you give me the billing cities for these invoices? | here are the billing cities of the invoices from the state in the USA with the most invoices | How about postal codes for these invoices?
SQL: SELECT DISTINCT billing_postal_code FROM invoices WHERE billing_state  =   ( SELECT billing_state FROM invoices WHERE billing_country   =   "USA" GROUP BY billing_state ORDER BY COUNT ( * )  DESC LIMIT 1 )