$\text{a) $\dfrac{-3}{5}$ + $\dfrac{5}{8}$ + $\dfrac{-2}{5}$ + $\dfrac{3}{8}$ }$
$\text{ = ( $\dfrac{-3}{5}$ - $\dfrac{2}{5}$ ) + ( $\dfrac{5}{8}$ + $\dfrac{3}{8}$ )}$
$\text{ = $\dfrac{-5}{5}$ + $\dfrac{8}{8}$ }$
$\text{ = -1 + 1 }$
$\text{ = 0 }$
$\text{ b) $\dfrac{-4}{15}$ . $\dfrac{5}{11}$ + $\dfrac{-4}{5}$ . $\dfrac{11}{6}$ }$
$\text{ = $\dfrac{-4}{5}$ . ( $\dfrac{5}{11}$ + $\dfrac{11}{6}$ )}$
$\text{ = $\dfrac{-4}{15}$ . $\dfrac{151}{66}$ }$
$\text{ = $\dfrac{-302}{495}$ }$