[tex]\it \overline{abc}-\overline{cba}=198 \Rightarrow 100a+10b+c-100c-10b-a=198 \Rightarrow \\ \\ \Rightarrow 99(a-c)=198|_{:99} \Rightarrow a-c=2 \Rightarrow \\ \\ \Rightarrow (a,\ c) \in\{(3,\ 1);\ (4,\ 2);\ (5,\ 3);\ (6,\ 4):\ (7,\ 5);\ (8,\ 6);\ (9,\ 7)\}\\ \\ b=\ orice\ cifr\breve a[/tex]