Решение:
$$ \frac{1}{3}x + 2\frac{2}{5} = 3\frac{2}{3} $$
$$ \frac{1}{3}x + \frac{12}{5} = \frac{11}{3} $$
$$ \frac{1}{3}x = \frac{11}{3} - \frac{12}{5} $$
$$ \frac{1}{3}x = \frac{55}{15} - \frac{36}{15} $$
$$ \frac{1}{3}x = \frac{19}{15} $$
$$ x = \frac{19}{15} * 3 $$
$$ x = \frac{19}{5} = 3,8 $$
Ответ: x = 3,8