How much less 2a² + 1 is than 3a² - 6 ?

If x = 6a + 8b + 9c; y = 2b - 3a - 6c and z = c - b + 3a; find :

(i) x + y + z

(ii) x - y + z

(iii) 2x - y - 3z

(iv) 3y - 2z - 5x

(9x⁴ - 12x³ - 18x) ÷ (3x) is equal to:

1. 3x³ + 4x² + 6

2. 3x³ + 4x² - 6

3. 3x³ - 4x² - 6

4. 3x⁴ - 4x² + 6