Answer:

Step-by-step explanation:

(13x - 11y + 9z) + (7z + 3x - 5y)

= 16x - 16y + 16z ---- 1

(6x - 7y - 5z) + (-4x - 9y + 6z) + (5x - 4y + 3z)

= 7x - 20y + 4z

7x - 20y + 4z - (16x - 16y + 16z)

7x - 20y + 4z - 16x + 16y - 16z

= - 9x  - 4y - 12z