28(x - 1) + 7x (x - 1)
= (x - 1)(28 + 7x)
= (x - 1)(7*4 + 7x)
= (x - 1)*7*(x + 4)
= 7(x - 1)(x + 4)

(2x - 1)(4x - 5) + 8x - 4
= (2x - 1)(4x - 5) + 4*2x - 4*1
= (2x - 1)(4x - 5) + 4(2x - 1)
= (2x - 1)(4x - 5 + 4)
= (2x - 1)(4x - 1)

6(x + 7)(3 - x) + 3(x + 7)(1 - x)
= 3(x + 7)*2*(3 - x) + 3(x + 7)(1 - x)
= 3(x + 7)[2(3 - x) + 1 - x]
= 3(x + 7)(6 - 2x + 1 - x)
= 3(x + 7)(-3x + 7) .

(x - 1)² + (3x - 3)(2x + 1)
= (x - 1)² + 3(x - 1)(2x + 1)
= (x - 1)[x - 1 + 3(2x + 1)]
= (x - 1)(7x + 2) .

(12x - 4) + 5x(3x - 1) + (x - 1)(9x - 3)
= (4*3x - 4) + 5x(3x - 1) + (x - 1)(3*3x - 3)
= 4(3x - 1) + 5x(3x - 1) + 3(x - 1)(3x - 1)
= (3x - 1)[4 + 5x + 3(x - 1)]
= (3x - 1)(8x + 1)

2x(4x + 6)(2x + 2) + 6x(2x + 3)(3x + 3) - 4x(6x + 9)(x + 1)
= 2x*2(2x + 3)*2*(x + 1) + 6x(2x + 3)*3*(x + 1) -4x*3*(2x + 3)(x + 1)
= (2x + 3)(x + 1)(8x + 18x - 12x)
= 14x(2x + 3)(x + 1) .