= 4a^6(3x - 2)(4x + 1)x + 125
= 4a^6(12x^2 + 3x - 8x - 2)x + 125
= 4a^6(12x^2 - 5x - 2)x + 125
= 48a^6x^3 - 20a^6x^2 - 8a^6x + 125