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

### Instruction:
What is the mean huc example code when the example name's lower snake, there are 6 digits, and less than 3 levels?

### Inputs:
table_name: table, columns: ['Name', 'Level', 'Digits', 'Average size (square miles)', 'Number of HUs (approximate)', 'Example name', 'Example code (HUC)']

### Response:
SELECT AVG Example code (HUC) FROM table WHERE Example name = lower snake AND Digits = 6 AND Level < 3