19) (7$$\frac{1}{3} - 6$$\frac{7}{8}$$):$$\frac{3}{4}$$-(5$$\frac{1}{4}$$-4$$\frac{21}{40}$$):1$$\frac{9}{20}$$ = ($$\frac{22}{3} - \frac{55}{8}$$) : $$\frac{3}{4}$$ - ($$\frac{21}{4} - \frac{181}{40}$$) : $$\frac{29}{20}$$ = ($$\frac{176 - 165}{24}$$) : $$\frac{3}{4}$$ - ($$\frac{210 - 181}{40}$$) : $$\frac{29}{20}$$ = $$\frac{11}{24} \cdot \frac{4}{3}$$ - $$\frac{29}{40} \cdot \frac{20}{29}$$ = $$\frac{11}{6} \cdot \frac{1}{3}$$ - $$\frac{1}{2}$$ = $$\frac{11}{18} - \frac{9}{18}$$ = $$\frac{2}{18}$$ = $$\frac{1}{9}$$
Ответ: $$\frac{1}{9}$$