Bonjour,
[tex]\dfrac{2}{3}-\dfrac{5}{3}\times\dfrac{3}{2}=\dfrac{2}{3}-\dfrac{5}{2}=\dfrac{4}{6}-\dfrac{15}{6}=\boxed{-\dfrac{11}{6}}[/tex]
[tex]\dfrac{-\dfrac{7}{4}+\dfrac{1}{2}}{\dfrac{2}{7}+\dfrac{1}{4}}=\dfrac{-\dfrac{7}{4}+\dfrac{2}{4}}{\dfrac{8}{28}+\dfrac{7}{28}}=\dfrac{-\dfrac{5}{4}}{\dfrac{15}{28}}=-\dfrac{5}{4}\times\dfrac{28}{15}=-\dfrac{140}{60}=\boxed{-\dfrac{7}{3}}[/tex]
[tex]\dfrac{-\dfrac{28}{5}}{-21}=\dfrac{28}{5}\times\dfrac{1}{21}=\dfrac{28}{105}=\boxed{\dfrac{4}{15}}[/tex]
