6. Calculează: a) (x³ - 2x² - 1) : x; b) (12x6 + 18x4 - 6x³): (6x³); c) (4ry³ - 2x²y - 4xy) : (2xy); d) (3xy³ - 6ay²-3y²): (3y²); e) (14r³y² - 7r³y) : (7z³y); f) (2xyz + 4x²z - 6xz²): (2xz).​