The denominator can be written xy+4y-(x+4)=y(x+4)-(x+4)=(y-1)(x+4).
However, the numerator x³y+4x²-y doesn’t factorise (so please check if this expression is the intended one). Moreover, neither y-1 nor x+4 is a factor of the numerator. If either were a factor then simplification would be possible.