А) {10(x+4)-y=6(y+x)

{6(x+y)=6(y-5)-12

{10x+40-y=6y+6x

{6x+6y=6y-30-12

{4x-7y= -40

{6x=-42

x= -7

y=(-7*4+40)/7= 12/7

ответ: (-7; 12/7) или (-7; 1 5/7)

Б) {(x+2y)/8 + (x-y)/2= 2 |•8

{(4x-4y)/14-(7x+6y)/7= 1  |•14

{x+2y+4(x-y)=16

{4x-4y-2(7x+6y)=14

{x+2y+4x-4y=16

{4x-4y-14x-12y=14

{5x-2y=16

{-10x-16y=14 |: -2

{5x-2y=16

{5x+8y= -7

5x-2y-5x-8y=16+7

-10y=23
y= -2,3

x= (16-4,6)/5= 2,28

ответ: (2,28; -2,3)