15) [(1$$\frac{1}{2}+2\frac{2}{3}):3\frac{3}{4}-\frac{2}{5}]:8\frac{8}{9}+\frac{1}{4}

15) [(1$$\frac{1}{2}+2\frac{2}{3}):3\frac{3}{4}-\frac{2}{5}]:8\frac{8}{9}+\frac{1}{4}$$ = [($$\frac{3}{2} + \frac{8}{3}$$) : $$\frac{15}{4} - \frac{2}{5}$$] : $$\frac{80}{9} + \frac{1}{4}$$ = [($$\frac{9 + 16}{6}$$) : $$\frac{15}{4} - \frac{2}{5}$$] : $$\frac{80}{9} + \frac{1}{4}$$ = [$$\frac{25}{6} \cdot \frac{4}{15} - \frac{2}{5}$$] : $$\frac{80}{9} + \frac{1}{4}$$ = [$$\frac{10}{9} - \frac{2}{5}$$] : $$\frac{80}{9} + \frac{1}{4}$$ = [$$\frac{50 - 18}{45}$$] : $$\frac{80}{9} + \frac{1}{4}$$ = $$\frac{32}{45} \cdot \frac{9}{80} + \frac{1}{4}$$ = $$\frac{4 \cdot 1}{5 \cdot 10} + \frac{1}{4}$$ = $$\frac{2}{25} + \frac{1}{4}$$ = $$\frac{8 + 25}{100}$$ = $$\frac{33}{100}$$

Ответ: $$\frac{33}{100}$$