Đáp án: $n\in\{24,15,12,9,8,7,5,4,3,0,-3,-12\}$
Giải thích các bước giải:
Để $6n-54\quad\vdots\quad n-6$
$\to 6n-36-18\quad\vdots\quad n-6$
$\to 6(n-6)-18\quad\vdots\quad n-6$
$\to 18\quad\vdots\quad n-6$
$\to n-6\in U(18)$
$\to n-6\in\{18,9,6,3,2,1,-1,-2,-3,-6,-9,-18\}$
$\to n\in\{24,15,12,9,8,7,5,4,3,0,-3,-12\}$