`a) ` $\dfrac{9}{7}$ `: x = `$\dfrac{3}{4}$
`⇔ x = ` $\dfrac{9}{7}$ `: ` $\dfrac{3}{4}$
`⇔ x = ` $\dfrac{9}{7}$ x $\dfrac{4}{3}$
`⇔ x = ` $\dfrac{12}{7}$
Vậy ` x = ` $\dfrac{12}{7}$
`b) x - ` $\dfrac{1}{6}$ `=` $\dfrac{13}{4}$ `-` $\dfrac{5}{2}$
`⇔ x - ` $\dfrac{1}{6}$ `=` $\dfrac{13}{4}$ `-` $\dfrac{10}{4}$
`⇔ x - ` $\dfrac{1}{6}$ `=` $\dfrac{3}{4}$
`⇔ x =` $\dfrac{3}{4}$ `+` $\dfrac{1}{6}$
`⇔ x =` $\dfrac{9}{12}$ `+` $\dfrac{2}{12}$
`⇔ x =` $\dfrac{11}{12}$
Vậy ` x =` $\dfrac{11}{12}$
