[tex]\it n\in\mathbb{N},\ \ n:6=7\ \ rest\ \ r \Rightarrow \begin{cases}\it n=6\cdot7+r \Rightarrow n=42+r\ \ \ (1)\\ \\ \it r<6\ \ \ \ \ \ (2)\end{cases}\\ \\ \\ (2) \Rightarrow r\in\{0,\ 1,\ 2,\ 3,\ 4,\ 5\}|_{+42} \Rightarrow n\in\{42,\ 43,\ 44,\ 45,\ 46,\ 47\}[/tex]
