Below is an instruction that describes a task. Write a response that appropriately completes the request.

### Instruction:
Which population has a GDP (nominal) of $6.4 billion?

### Inputs:
table_name: table, columns: ['Country', 'Population', 'Area (km²)', 'GDP (nominal)', 'GDP per capita (nominal)']

### Response:
SELECT Population FROM table WHERE GDP (nominal) = $6.4 billion