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

### Instruction:
What is the attendance in a week earlier than 4, and result is w 31-20?

### Inputs:
table_name: table, columns: ['Week', 'Date', 'Opponent', 'Result', 'Attendance']

### Response:
SELECT AVG Attendance FROM table WHERE Week < 4 AND Result = w 31-20