\(a,\dfrac{3}{4}-\dfrac{2}{5}+\dfrac{5}{12}=\dfrac{45}{60}-\dfrac{24}{60}+\dfrac{25}{60}=\dfrac{46}{60}=\dfrac{23}{30}\\ b,\dfrac{15}{7}-\dfrac{4}{3}-\dfrac{2}{9}=\dfrac{135}{63}-\dfrac{84}{63}-\dfrac{14}{63}=\dfrac{37}{63}\\ c,\dfrac{3}{5}+\dfrac{2}{5}\times\dfrac{4}{5}=\dfrac{15}{25}+\dfrac{8}{25}=\dfrac{23}{25}\\ d,\dfrac{4}{5}-\left(\dfrac{6}{15}+\dfrac{1}{5}\right)=\dfrac{4}{5}-\dfrac{1}{5}-\dfrac{2}{5}=\dfrac{1}{5}\)