$B=\dfrac{\dfrac{8}{3}-\dfrac{12}{5}+\dfrac{28}{11}}{\dfrac{14}{3}-\dfrac{21}{5}+\dfrac{49}{11}}$
$=\dfrac{\dfrac{4.2}{3}-\dfrac{4.3}{5}+\dfrac{4.7}{11}}{\dfrac{7.2}{3}-\dfrac{7.3}{5}+\dfrac{7.7}{11}}$
$=\dfrac{4(\dfrac{2}{3}-\dfrac{3}{5}+\dfrac{7}{11})}{7(\dfrac{2}{3}-\dfrac{3}{5}+\dfrac{7}{11})}$
$=\dfrac{4}{7}$
Chúc bạn học tốt !!!!
