* **G1 (Total sales):** $110,000
* **1A (GST on sales):** $10,000  
  *Working: $110,000 / 11 = $10,000*
* **1B (GST on purchases):** $6,000  
  *Working: $66,000 / 11 = $6,000*
* **W2 (Amounts withheld):** $8,000  
  *Working: $40,000 × 20% = $8,000*
* **Net amount payable to the ATO:** $12,000  
  *Working: (1A - 1B) + W2 = ($10,000 - $6,000) + $8,000 = $4,000 + $8,000 = $12,000*