Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_name_31 (rank INTEGER, headquarters VARCHAR, market_value__billion_$_ VARCHAR)

### Question ###
What is the average rank for USA when the market value is 407.2 billion?

### Accurate SQL ###

SELECT AVG(rank) FROM table_name_31 WHERE headquarters = "usa" AND market_value__billion_$_ > 407.2