{х/6+у/4=6 {х/8-у/2=-1

( х/6 ) + ( y/4 ) = 6
( x/8 ) - ( y/2 ) = - 1 
( 4x/24 ) + ( 6y/24 ) = 144/24 
( 3x/24 ) - ( 12y/24 ) = - 24/24
4x + 6y = 144 
3x - 12y = - 24
8x + 12y = 288
3x + 8x - 12y + 12y = - 24 + 288
11x = 264 
x = 24 
3x - 12y = - 24 
3*24 - 12y = - 24 
- 12y = - 24 - 72 
y = 96 : 12 
y = 8 
Ответ ( 24 ; 8 )