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

### Instruction:
What is the average weeks of a song with a larger than 3 position after 1977?

### Inputs:
table_name: table, columns: ['Year', 'Single', 'Chart', 'Position', 'Weeks on chart']

### Response:
SELECT AVG Weeks on chart FROM table WHERE Position > 3 AND Year > 1977