| BAS label | Working | Amount |
|---|---:|---:|
| G1 | Total GST-inclusive sales | **$110,000** |
| 1A | $110,000 ÷ 11 | **$10,000** |
| 1B | $66,000 ÷ 11 | **$6,000** |
| W2 | $40,000 × 20% | **$8,000** |

**Net amount payable to the ATO:**

\[
(\$10,000-\$6,000)+\$8,000=\boxed{\$12,000}
\]