Вопрос в картинках...

$\frac{8}{15} (3 \: \frac{3}{4} m - \frac{5}{16} n) - \frac{3}{20} (6 \: \frac{2}{3} m - 4 \: \frac{4}{9} ) = \frac{8}{15} ( \frac{15}{4} m - \frac{5}{16} n) - \frac{3}{20}( \frac{20}{3} m - \frac{40}{9} n) = \\ \\ = 2m - \frac{1}{6} n - m + \frac{2}{3} n = m - \frac{1}{6}n + \frac{2 \times 2}{3 \times 2}n = m - \frac{1}{6} n + \frac{4}{6} n = \\ \\ \\ = m + \frac{3}{6} n = m + 0.5n$

Ответ: m+0,5n