19) 8/15 (3/4 x - 5/16 y) - 2/3 (6/5 x - 4/9 y) =

19) $$\frac{8}{15} (\frac{3}{4} x - \frac{5}{16} y) - \frac{2}{3} (\frac{6}{5} x - \frac{4}{9} y) = \frac{8}{15} \cdot \frac{3}{4} x - \frac{8}{15} \cdot \frac{5}{16} y - \frac{2}{3} \cdot \frac{6}{5} x + \frac{2}{3} \cdot \frac{4}{9} y = \frac{24}{60} x - \frac{40}{240} y - \frac{12}{15} x + \frac{8}{27} y = \frac{2}{5} x - \frac{1}{6} y - \frac{4}{5} x + \frac{8}{27} y = \frac{2}{5} x - \frac{4}{5} x - \frac{1}{6} y + \frac{8}{27} y = - \frac{2}{5} x - \frac{9}{54} y + \frac{16}{54} y = - \frac{2}{5} x + \frac{7}{54} y$$

Ответ: $$- \frac{2}{5} x + \frac{7}{54} y$$