8.-2m+3n-6; 3m-8n+8; -5m+n-10

9. -5a-2b-3c; 7a-3b+5c; -8a+5b-3c

10. ab+bc+cd; -8ab-3bc-3cd; 5ab+2bc+2cd


11. ax-ay-az; -5ax-7ay-6az; 4ax+9ay +8az


12. 5x-7y+8; −y+6-4x; 9-3x+8y​