Помог те конвертировать

а) ((3a+1)/(3a-1) - (3a-1)/(3a+1)):4a/(15a+5) =

= (9a+6a+1-9a+6a-1)/((3a-1)(3a+1)) (5(3a+1))/4a =

= (12a5(3a+1))/((3a-1)(3a+1)4a)=15/3a-1

б) y/(x+1) (1-x)/(y-1)-(1-xy)/(y-1) =

= y/(x+1) ((1-x)(x+1))/(y-1) - (1-xy)/(y-1) =

= (y-xy-1+xy)/(y-1) =

= ((y-1)(y+1))/(y-1) = y+1