a ) `x` : `4/7` = `7/12` - `1/3` b) `9/12` x `x` + `1/4` x `x` = `3/4` c) `4/5` x `x` = `7/5` : `3/14` mn giúp e với ạ

a) x : $\dfrac{4}{7}$ = $\dfrac{7}{12}$ - $\dfrac{1}{3}$

    x : $\dfrac{4}{7}$ = $\dfrac{1}{4}$

    x = $\dfrac{1}{4}$ $\times$ $\dfrac{4}{7}$

    x = $\dfrac{1}{7}$

b) $\dfrac{9}{12}$ $\times$ x + $\dfrac{1}{4}$ $\times$ x = $\dfrac{3}{4}$

    x $\times$ ($\dfrac{9}{12}$ + $\dfrac{1}{4}$) = $\dfrac{3}{4}$

    x $\times$ 1 = $\dfrac{3}{4}$

    x = $\dfrac{3}{4}$ : 1

    x = $\dfrac{3}{4}$

c) $\dfrac{4}{5}$ $\times$ x = $\dfrac{7}{5}$ : $\dfrac{3}{14}$

   $\dfrac{4}{5}$ $\times$ x = $\dfrac{98}{15}$

   x = $\dfrac{98}{15}$ : $\dfrac{4}{5}$

   x = $\dfrac{49}{6}$

$\frac{9}{12}$x x + $\frac{1}{4}$  x x = $\frac{3}{4}$ 

→$\frac{3}{4}$ x  x + $\frac{1}{4}$ x  x = $\frac{3}{4}$ ←

Tầng 2 mình làm thành cơ bản rùi nha!