No 2 gimana caranya?

7 = x+3y
9 = 2x+y

7 = x+3y
27 = 6x+3y
__________ -
-20 = -5x
4 = x

7 = x+3y
7 = 4+3y
3 = 3y
1 = y

2x + y = 9
x + 3y = 7
maka y= -2x+9
x + 3y= 7
x+3(-2x+9)=7
x+-6x+27=7
-5x=-20
x= 4

maka :
x+3y = 7
4+3y=7
3y=7-4
y=1