a: \(=\dfrac{15}{16}\cdot\dfrac{8}{3}\cdot\dfrac{3}{4}=\dfrac{15}{16}\cdot2=\dfrac{15}{8}\)
b \(=\dfrac{17}{4}:\left(\dfrac{4}{3}\cdot\dfrac{21}{4}\right)=\dfrac{17}{4}:7=\dfrac{17}{28}\)
c: \(=\dfrac{3}{4}+\dfrac{1}{20}=\dfrac{15}{20}+\dfrac{1}{20}=\dfrac{16}{20}=\dfrac{4}{5}\)


