a. $x$ + $\frac{2}{5}$ = $\frac{1}{2}$
$x$ = $\frac{1}{2}$ - $\frac{2}{5}$
$x$ = $\frac{5}{10}$ - $\frac{4}{10}$
$x$ = $\frac{1}{10}$
b. $x$ - $\frac{2}{5}$ = $\frac{2}{7}$
$x$ = $\frac{2}{7}$ + $\frac{2}{5}$
$x$ = $\frac{10}{35}$ + $\frac{14}{35}$
$x$ = $\frac{24}{35}$
c. $x$ x $\frac{3}{4}$ = $\frac{9}{20}$
$x$ = $\frac{9}{20}$ : $\frac{3}{4}$
$x$ = $\frac{3}{5}$
d. $x$ : $\frac{1}{7}$ = 14
$x$ = 14 x $\frac{1}{7}$
$x$ = 2