\(a,\left(-\dfrac{13}{7}-\dfrac{4}{9}\right)-\left(-\dfrac{10}{7}-\dfrac{4}{9}\right)\\ =-\dfrac{13}{7}-\dfrac{4}{9}+\dfrac{10}{7}+\dfrac{4}{9}\\ =-\dfrac{3}{7}.\)
a) $(-\frac{13}{7}-\frac49)-(-\frac{10}{7}-\frac49)$
$=-\frac{13}{7}-\frac49+\frac{10}{7}+\frac49$
$=(-\frac{13}{7}+\frac{10}{7})+(-\frac49+\frac49)$
$=\frac{-3}{7}$