(5x4 – 3x2 + 4) + (6x3 – 4x2 – 7)

2. (8a – 15b – 5c) + (–9a + 8b – 8c)

3. (25x2 – 9x + 5) + (12x2 + 7x –9)

4. (5x3 – 7x2 + 3x – 4) – (8x3 + 2x2 + 3x – 7)

5. (35m2 + 16mn –36n2) – (9m2 + 42mn + 4n2 –20)​