$a$) ` 4x.(5x+2) - (10x-3).(2x+7) = 133`
`⇔ 20x^2 + 8x - (20x^2 - 6x + 70x - 21) = 133`
`⇔ 20x^2 + 8x - 20x^2 + 6x - 70x + 21 = 133`
`⇔ -56x =112`
`⇔ x = -2`
Vậy `x=-2`
$b$) `3.(6x-5).(4x+1) - (8x+3).(9x-2) = 203`
`⇔ (18x-15).(4x+1) - (72x^2 + 27x - 16x - 6) = 203`
`⇔ (72x^2 - 60x + 18x - 15) - 72x^2- 27x + 16x + 6= 203`
`⇔ -53x= 212`
`⇔ x = -4`
Vậy `x=-4`.