1) 12a³ – 16a² = 4a²(3a – 4)

2) 5m² + 15m³ – 20m⁵ = –5m²(4m³ – 3m – 1) = –5m²(m – 1)(4m² + 4m + 1) = –5m²(m – 1)(2m + 1)²

3) m(a – 3) – n(a – 3) = (m – n)(a – 3)

4) 9m + 9n + mn + n² = m(n + 9) + n(n + 9) = (m + n)(n + 9)