`a) 2x + 8 = 4 - 4x`

`=> 2x + 4x = 4 - 8`

`=> 6x = -4`

`=> x = -2/3`

Vậy `x = -2/3`

`b) -x(2x + 6) = 5x + 3(x - 5)`

`=> -2x^2 - 6x = 5x + 3x - 15`

`=> -2x^2 - 6x - 8x + 15 = 0`

`=> 2x^2 + 14x - 15 = 0`

`=> x = (-7 +- \sqrt{79})/2`

Vậy `x = (-7 +- \sqrt{79})/2`