a. \(-3\dfrac{3}{4}+\dfrac{-10}{25}+\dfrac{-6}{12}\)
= \(\dfrac{-9}{4}+\dfrac{-10}{25}+\dfrac{-6}{12}\)
= \(\dfrac{-675}{300}+\dfrac{-120}{300}+\dfrac{-150}{300}\)
= \(\dfrac{-675+\left(-120\right)+\left(-150\right)}{300}\)
= \(\dfrac{-945}{300}=\dfrac{-63}{20}\)
b. \(4-1\dfrac{2}{5}-\dfrac{8}{3}\)
= \(4-\dfrac{7}{5}-\dfrac{8}{3}\)
= \(\dfrac{60}{15}-\dfrac{21}{15}-\dfrac{40}{15}\)
= \(\dfrac{60-21-40}{15}\)
= \(\dfrac{-1}{15}\)
c. \(-\dfrac{5}{12}+1\dfrac{5}{18}-2,25\)
= \(\dfrac{-5}{12}+\dfrac{23}{18}-2,25\)
= \(\dfrac{-15}{36}+\dfrac{46}{36}-\dfrac{81}{36}\)
= \(\dfrac{-15+46+81}{36}\)
= \(\dfrac{112}{36}=\dfrac{28}{9}\)