1/x-1/y=3
(y-x)/xy=3
y-x=3xy
x-y=-3xy
(5x+2xy-5y)/(x-4xy-y )
=[5(x-y)+2xy]/[(x-y)-4xy]
=[5*(-3xy)+2xy]/(-3xy-4xy)
=-13xy/(-7xy)
=13/7