$\frac{2}{3}х + \frac{4}{9}х = 3,2$
$(\frac{6}{9} + \frac{4}{9})х = 3,2$
$\frac{10}{9}х = \frac{32}{10}$
$х = \frac{32}{10} : \frac{10}{9}$
$х = \frac{32}{10} * \frac{9}{10}$
$х = \frac{288}{100} = 2,88$

$\frac{5}{12}х - \frac{4}{15}х = 0,51$
$(\frac{25}{60} - \frac{16}{60})х = \frac{51}{100}$
$\frac{9}{60}х = \frac{51}{100}$
$х = \frac{51}{100} : \frac{3}{20}$
$х = \frac{51}{100} * \frac{20}{3}$
$х = \frac{17}{5} * \frac{1}{1} = \frac{34}{10} = 3,4$

$х - 0,2х = \frac{8}{15}$
$(1 - 0,2)х = \frac{8}{15}$
$0,8х = \frac{8}{15}$
$х = \frac{8}{15} : \frac{8}{10}$
$х = \frac{8}{15} * \frac{10}{8}$
$х = \frac{1}{3} * \frac{2}{1} = \frac{2}{3}$