Ответ:

\[\frac{xy(x-y)(x+y)}{-2(x-y)}\cdot\frac{3(x-y)}{(x-y)(x+y)}=-\frac{3xy}{2}.\]

При \(x=4, y=\frac14\): \(-\frac{3\cdot4\cdot\frac14}{2}=-\frac32\).

Ответ: \(-\frac32\).