Решите уравнения, поажалуйста

Решите задачу:

$a)21 {x}^{2} + 3x - 7x - 1 - 21 {x }^{2} - 3 = 0 \\ - 4x - 4 = 0 \\ - 4(x + 1) = 0 \\ x = - 1 \\ b)1 - 3x - 4x + 12 {x}^{2} - 12 {x}^{2} + 6x = 0 \\ - x + 1 = 0 \\ x = 1 \\ c)12 - 4x - 24x + 8 {x}^{2} - x - 8 {x}^{2} = 0 \\ - 29x + 12 = 0 \\ x = \frac{12}{29} \\ d)4 - 4y - 6y + 6 {y}^{2} - 6 {y}^{2} + 3y - 2y + 1 - 3 = 0 \\ - 9y + 2 = 0 \\ y = \frac{2}{9}$