\(\dfrac{3}{28}\) ≤ \(\dfrac{x}{56}\) ≤ \(\dfrac{1}{4}\)
\(\dfrac{6}{56}\) ≤ \(\dfrac{x}{56}\) ≤ \(\dfrac{14}{56}\)
6 ≤ \(x\) ≤ 14
Vì \(x\) nguyên nên \(x\) \(\in\) {6; 7; 8; 9; 10; 11; 12; 13; 14}
Vậy \(x\) \(\in\) {6; 7; 8; 9; 10; 11; 12; 13; 14}