factoring:
your equation: x^-4xy+3y^
now figure out what adds to -4 and multiplied to +3 (-3&-1)
use that information to factor.
you get: (x-3y)(x-y)
now use the distributive property to make sure it's the right answer: x^-xy-3xy+3y^
this means (x-3y)(x-y) is correct.
hope this helped :)