`a)`
`(2x-3)^2 - (x-3) ^3 + (4x+1)(16x^2 -1)`
`= [ (2x)^2 - 2 . 2x . 3 + 3^2] - (x^3 - 3 . x^2 . 3 + 3 . x . 3^2 - 3^3) + (64x^3 - 4x + 16x^2 - 1)`
` = (4x^2 - 12x + 9) - (x^3 - 9x^2 + 27x - 27) + (64x^3 - 4x + 16x^2 - 1)`
`= 4x^2 - 12x + 9 - x^3 + 9x^2 - 27x + 27 + 64x^3 - 4x + 16x^2 - 1`
`= (64x^3-x^3) + (4x^2 + 9x^2 + 16x^2) - (27x + 12x + 4x) + (27+9-1)`
`= 63x^3 + 29x^2 - 43x + 35`
`b)`
`(2x-y)(4x^2 + 2xy + y^2) - (3x+y)^3 + (x-2y)`
`= (2x-y) [ (2x)^2 + 2x . y + y^2] - [ (3x)^3 + 3 . (3x)^2 . y + 3 . 3x . y^2 + y^3] + x-2y`
`= [ (2x)^3 - y^3] - (27x^3 + 27^2y + 9y^2 + y^3) + x - 2y`
`= 8x^3 - y^3 - 27x^3 - 27x^2y - 9y^2 - y^3 + x -2y`
`= (8x^3 - 27x^3) - (y^3+ y^3) - 27x^2y - 9y^2 + x - 2y`
`= -19x^3 - 2y^3 - 27x^2y - 9y^2 + x - 2y`
