câu `1` :
a) $\dfrac{7}{9}$ `+` $\dfrac{3}{9}$ `=` $\dfrac{10}{9}$
b)$\dfrac{2}{3}$ `-` $\dfrac{3}{8}$ `=` $\dfrac{7}{24}$
câu `2` :
`x` `-` $\dfrac{3}{4}$ `=` $\dfrac{1}{2}$
`x` `=` $\dfrac{1}{2}$ `+` $\dfrac{3}{4}$
`x ` `=` $\dfrac{5}{4}$
vậy `x` `=` $\dfrac{5}{4}$