$(5) 3-1\dfrac{1}{2}=x+\dfrac{1}{7}$
$\dfrac{3}{2}=x$
$\dfrac{3}{2}-\dfrac{1}{7}=x$
$\dfrac{19}{14}=x$
Vậy $x=\dfrac{19}{14}$
$(6) \dfrac{4}{5}+(\dfrac{-1}{9})=\dfrac{8}{7}-x$
$\dfrac{31}{45}=\dfrac{8}{7}-x$
$\dfrac{8}{7}-\dfrac{31}{45}=x$
$x=\dfrac{143}{315}$
Vậy $x=\dfrac{143}{315}$