A = 3 x + 6 + 49 - 42 x + 28 x - 6 x²
= - 6 x² - 11 x + 55
B = 4 x + 36 - ( 7 x + 7 + x² + x )
= 4 x +36 - 8 x - 7 - x²
= - x² - 4 x + 29
C = - 2 + 6 x - ( 3 x² - 15 x + 2 x - 10 )
= - 2 + 6 x - 3 x² + 13 x + 10
- 3 x² + 19 x + 8
D = - 3 a² - 6 - ( 2 a² + 7 a - 6 a - 21 )
= - 3 a² - 6 - 2 a² - 7 a + 6 a + 21
= - 5 a² - a + 15
