А) 3 а+3+na+n

б) 6 мх-2 м+18 х-6

в) ах+3 х+2 а+6

г) 2 мх-3 м+10 х-15

(3a+3) + (na+n) = 3 (a+1) + n (a+1) = (a+1) (3+n); (6mx-2m) + (18x-6) = 2m (3x-1) + 6 (3x-1) = (3x-1) (2m+6); (ax+3x) + (2a+6) = x (a+3) + 2 (a+3) = (a+3) (x+2); (2mx+10x) - (3m+15) = 2x (m+5) - 3 (m+5) = (m+5) (2x-3).