@nguyenngoclananhpt
a, $(-2)$. $\frac{-38}{21}$ . $\frac{-7}{4}$ . $\frac{-3}{8}$
= $\frac{76}{21}$. $\frac{-7}{4}$ . $\frac{-3}{8}$
= $\frac{-19}{3 }$ . $\frac{-3}{8}$
= $\frac{19}{8}$
b, $\frac{7}{23}$ . ( $\frac{-8}{6}$ - $\frac{45}{18}$ )
= $\frac{7}{23}$ . - $\frac{-23}{6}$
= $\frac{-7}{6}$