12х+(6-3х) = 12х + 6-3х = 9х+6
(3,1-у)-(4-1,3у)= 3,1-у-4+1,3у = -0,9+2,1у
(х-у)-(-2х-3у)= х-у+2х+3у= 3х+2у
4(2а-2)+3(6-3а) = 8а-8 + 18-9а = -а +10
12х+(6-3х) = 12х + 6-3х = 9х+6
(3,1-у)-(4-1,3у)= 3,1-у-4+1,3у = -0,9+2,1у
(х-у)-(-2х-3у)= х-у+2х+3у= 3х+2у
4(2а-2)+3(6-3а) = 8а-8 + 18-9а = -а +10