We can use the properties of logarithms to simplify this expression:

log5 (35/3) + log5 (75/7)
= log5 (35) - log5 (3) + log5 (75) - log5 (7)
= log5 (35) + log5 (75) - log5 (3) - log5 (7)
= log5 (3575) - log5 (37)
= log5 (2625) - log5 (21)

Therefore, the simplified expression is log5 2625 - log5 21.