$\text{Đáp án:}$
a) $\dfrac{5}{15}+$ $\dfrac{4}{12}+$ $\dfrac{1}{7}$ $+$ $\dfrac{1}{-6}$
$=\dfrac{2}{3}$ $+$ $\dfrac{1}{7}$ $+$ $\dfrac{1}{-6}$
$=\dfrac{17}{21}$ $+$ $\dfrac{1}{-6}$
$=\dfrac{9}{14}$
b) $(\dfrac{-1}{5}-$$\dfrac{3}{12}$$ )+$ $\dfrac{-3}{4}$
$=$ $\dfrac{-9}{20}+$$\dfrac{-3}{4}$
$=\dfrac{-6}{5}$
$\text{Mong bn cho mk câu trl hay nhất ạ!!!}$