{X*3-y*3=26 {x*3+y*3=27

{x=26/3+y
{x*3+y*3=27

(26/3+y)*3+y*3=27

y=1/6

x*3+1/6*3=27
x=53/6

(x,y)=(53/6;1/6)

{53/6*3-1/6*3=26
{53/6*3+1/6*3=27

{26=26
{27=27

Ответ: (x,y)=(53/6;1/6)