$b,\dfrac{x}{3}-\dfrac{1}{2}=\dfrac{1}{5}$
$⇒\dfrac{x}{3}=\dfrac{1}{5}+\dfrac{1}{2}$
$⇒\dfrac{x}{3}=\dfrac{7}{10}$
$⇒x=\dfrac{7}{10}.3$
$⇒x=\dfrac{21}{10}$
$c,\dfrac{x}{5}+\dfrac{1}{2}=\dfrac{6}{10}$
$⇒\dfrac{x}{5}=\dfrac{6}{10}-\dfrac{1}{2}$
$⇒\dfrac{x}{5}=\dfrac{1}{10}$
$⇒x=\dfrac{1}{10}.5$
$⇒x=\dfrac{5}{10}$
$⇒x=\dfrac{1}{2}$