e) \frac{3x^{2}+6xy+3y^{2}}{12y^{2}-12x^{2}} = \frac{3(x+y)^{2}}{12(y^{2}-x^{2})} = \frac{3(x+y)^{2}}{12(y-x)(y+x)} = \frac{x+y}{4(y-x)}
Ответ: \frac{x+y}{4(y-x)}