a) $x$ + $\frac{1}{4}$ = $\frac{5}{8}$
$x$ = $\frac{5}{8}$ - $\frac{1}{4}$
$x$ = $\frac{5}{8}$ - $\frac{2}{8}$
$x$ = $\frac{3}{8}$
b) $x$ - $\frac{1}{3}$ = $\frac{1}{6}$
$x$ = $\frac{1}{6}$ + $\frac{1}{3}$
$x$ = $\frac{1}{6}$ + $\frac{2}{6}$
$x$ = $\frac{1}{4}$
c) $x$ x $\frac{3}{5}$ = $\frac{9}{10}$
$x$ = $\frac{9}{10}$ : $\frac{3}{5}$
$x$ = $\frac{9}{10}$ x $\frac{5}{3}$
$x$ = $\frac{3}{2}$
d) $x$ : $\frac{1}{6}$ = 18
$x$ = 18 x $\frac{1}{6}$
$x$ = 3