6(0,7х+2)+1,4(3у+4)=
х+у=5

{6(0.7х + 2) + 1.4(3у + 4)= 5      { 4.2x + 12 + 4.3y + 5.6 = 5
                                                :                                                 :
{x+y=5                                        { x + y=5
{4.2x + 4.3y = 5 - 12 - 5.6     { 4.2x + 4.3y = -13.6   {4.2( 5 - y) + 4.3y = -13.6
                                           ;                                   ;                                          ;
{x + y =5                               { x = 5 - y                     { x = 5 -y
{21 - 4.2y + 4.3y = -13.6    { 0.1y = -34.6  { y = -346            { y = -346
                                        ;                        ;                        ;
{ x = 5 - y                            { x = 5 - y        { x = 5 - (-346)    { x = 351
ответ ( 351 ; -346)