a. $\frac{-1}{6}$ + 0,75 = $\frac{-1}{6}$ + $\frac{3}{4}$ = $\frac{-2}{12}$ + $\frac{9}{12}$ = $\frac{7}{12}$
b. $3\frac{1}{10}$ - $\frac{3}{8}$ = $\frac{-31}{10}$ - $\frac{3}{8}$ = $\frac{-124}{40}$ - $\frac{15}{40}$ = $\frac{109}{40}$
c. 0,1 + $\frac{-9}{17}$ - (-0,9) = $\frac{1}{10}$ + $\frac{-9}{17}$ + $\frac{9}{10}$ = $\frac{1}{10}$ + $\frac{9}{10}$ + $\frac{-9}{17}$ = 1 + $\frac{-9}{17}$ = $\frac{8}{17}$