(31/20-26/45) . -36/35<x< (51/56+8/21+1/3) . 8/15
$(\dfrac{31}{20}-\dfrac{26}{45}).\dfrac{-36}{35}=\dfrac{279-104}{180}.\dfrac{-36}{35}=\dfrac{175}{180}.\dfrac{-36}{35}=\dfrac{35}{36}.\dfrac{-36}{35}=-1$
$(\dfrac{51}{56}+\dfrac{8}{21}+\dfrac{1}{3}).\dfrac{8}{15}=\dfrac{153+64+56}{168}.\dfrac{8}{15}=\dfrac{273}{168}.\dfrac{8}{15}=\frac{13}{8}.\dfrac{8}{15}=\dfrac{13}{15}$
$\Rightarrow -1<x<\dfrac{13}{15}$. Mà $x\in \mathbb{Z}\Rightarrow x=0$