a/
$BCNN:48$
$\dfrac3{16}=\dfrac{3.3}{16.3}=\dfrac9{48}$
$\dfrac5{24}=\dfrac{5.2}{24.2}=\dfrac{10}{48}$
b/
$BCNN:60$
$\dfrac3{20}=\dfrac{3.3}{20.3}=\dfrac9{60}$
$\dfrac{11}{30}=\dfrac{11.2}{30.2}=\dfrac{22}{60}$
$\dfrac7{15}=\dfrac{7.4}{15.4}=\dfrac{28}{60}$