42) \(\frac7{3a-3b}-\frac5{2a-2b}\)

\(\frac7{3(a-b)}-\frac5{2(a-b)}=\frac{14-15}{6(a-b)}=-\frac1{6(a-b)}\).

Ответ: \(-\frac1{6(a-b)}\).