1. -21b³-14b² = -7b²(3b+2) 2. mn+3m-n²-3n = n(m-n)+3(m-n) = (m-n)(n+3) 3. 81a²-b² = (9a-b)(9a+b) 4. 3y³-36y²+108y = 3y(y²-12y+36)