(6x - y) (3x - y + z)

18x²-6xy+12x-3xy+y²-yz
18x²-6xy-3xy+12x+y²-yz
18x²-9xy+12x+y²-yz

(6x - y)(3x - y + z)
= (6x × 3x) + (6x × (- y)) + (6x × z) + ((- y) × 3x) + ((- y) × (- y)) + ((- y) × z)
= 18x² - 6xy + 6xz - 3xy + y² - yz
= 18x² - 6xy - 3xy + 6xz + y² - yz
= 18x² - 9xy + 6xz + y² - yz

Maaf Kalau Salah