The answer will be 1.
Let Language G = {aba}.
prefix(G) = { ε, a, ab, aba}
suffix(G) = {ε, a , ba, aba}
(prefix(G) ∩ suffix(G) ) = { ε, a, aba}
(prefix(G) ∩ suffix(G) ) / G = { ε}
==> { ε, a, aba} / { aba} ( when we divide aba to aba it will be result ε)
Some exa:
1. { cat, rat, chat} / {at} ===> { c, r,ch}.
2.{cat, rat, group} / { at} ===> { c, r}
3.{cat, rat} / {cat} ===> { ε}.
4.{apple} / {e, le} ==> { appl, app}
So, the number of string = 1.