Răspuns:
a={ 0, 3, 6, 9 }
705, 735, 765, 795.
[tex]\it 3|\overline{7a5} \Rightarrow 3|(7+a+5) \Rightarrow 3|(12+a) \Rightarrow a\in\{0,\ \ 3,\ \ 6,\ \ 9\}[/tex]