Question 828542
x-y=12
x=12+y
x/y=3/7
x=3y/7
x=12+y
3y/7=12+y
3y=84+7y
-4y=84
y=-21
x=-9

or
y-x=12
y=12+x
x/y=3/7
y=7x/3
12+x=7x/3
36+3x=7x
36=4x
9=x
y=21