a)$\dfrac{2}{5}<\dfrac{x}{5}<\dfrac{6}{5}$
$⇔\dfrac{2}{5}.5<x<\dfrac{6}{5}.5$
$⇔2<x<6$
$⇔x=3;4;5$
b)$\dfrac{3}{4}<\dfrac{x}{12}<\dfrac{7}{6}$
$⇔\dfrac{3}{4}.12<x<\dfrac{7}{6}.12$
$⇔9<x<14$
$⇔x=10;11;12;13$
c)$\dfrac{-13}{9}<\dfrac{x}{72}<\dfrac{-11}{8}$
$⇔\dfrac{-13}{9}.72<x<\dfrac{-11}{8}.72$
$⇔−104<x<−99$
$⇔x=-103;102;101;.........-98$