3a-(2c-(6a-(c-b)+c+(a+8b-c))) = 3a-(2c-(6a-c+b+c+a+8b-c)) =
= 3a-(2c-(7a+9b-c)) = 3a-(2c-7a-9b+c) = 3a-(3c-7a-9b) = 10a+9b-3c
2,5+(-3,8)b+(-7,3)a+15+4b+4,8a = 2,5-3,8b-7,3a+15+4b+4,8a =
= 0,2b-2,5a+17,5
-3(2a-6b+8)+2(a-3b-9,4) = -6a+18b-24+2a-6b-18,8 = 12b-4a-42,8