1/x-1/y=3
1/ (1/x-1/y) = 1/3
3xy = y-x
2x+3xy-2y/x-xy-y
=(2x + y - x - 2y) / (x - y/3 + x/3 -y)
=(x-y) / (4x/3 - 4y/3)
= 4/3