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