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

### Instruction:
How many Gold medals for the Nations with 6 or more Bronze medals and 18 or more Silver?

### Inputs:
table_name: table, columns: ['Rank', 'Nation', 'Gold', 'Silver', 'Bronze', 'Total']

### Response:
SELECT AVG Gold FROM table WHERE Bronze > 6 AND Silver > 18