a. 5,75 . $\frac{-8}{9}$ = $\frac{23}{4}$ . $\frac{-8}{9}$ = $\frac{-46}{9}$
b. $2\frac{3}{8}$ . (-0,4) = $\frac{19}{8}$ . $\frac{-2}{5}$ = $\frac{-19}{20}$
c. $\frac{-12}{5}$ : (-6,5) = $\frac{-12}{5}$ : $\frac{-13}{2}$ = $\frac{-12}{5}$ . $\frac{-2}{13}$ = $\frac{24}{65}$