и) $$\frac{2}{5}z + \frac{2}{3}z - \frac{7}{15}z = 2\frac{1}{2}$$;

и) $$\frac{2}{5}z + \frac{2}{3}z - \frac{7}{15}z = 2\frac{1}{2}$$

$$ \frac{2 \cdot 3}{5 \cdot 3}z + \frac{2 \cdot 5}{3 \cdot 5}z - \frac{7}{15}z = \frac{5}{2} $$

$$ \frac{6}{15}z + \frac{10}{15}z - \frac{7}{15}z = \frac{5}{2} $$

$$ \frac{6+10-7}{15}z = \frac{5}{2} $$

$$ \frac{9}{15}z = \frac{5}{2} $$

$$ \frac{3}{5}z = \frac{5}{2} $$

$$ z = \frac{5}{2} : \frac{3}{5} $$

$$ z = \frac{5}{2} \cdot \frac{5}{3} $$

$$ z = \frac{5 \cdot 5}{2 \cdot 3} $$

$$ z = \frac{25}{6} $$

$$ z = 4\frac{1}{6} $$

Ответ: 4$$\frac{1}{6}$$