\(a.\dfrac{1}{6}+\dfrac{1}{14}=\dfrac{14}{84}+\dfrac{6}{84}=\dfrac{20}{84}=\dfrac{5}{21}\\ b.\dfrac{1}{3}+\dfrac{4}{5}=\dfrac{5}{15}+\dfrac{12}{15}=\dfrac{17}{15}\)
\(\dfrac{1}{6}+\dfrac{1}{14}=\dfrac{14}{84}+\dfrac{6}{84}=\dfrac{5}{21}\)
\(\dfrac{1}{3}+\dfrac{4}{5}=\dfrac{5}{15}+\dfrac{12}{15}=\dfrac{17}{15}\)