a) $$2\frac{4}{15} + 1\frac{71}{80} + 3\frac{11}{15} = (2\frac{4}{15} + 3\frac{11}{15}) + 1\frac{71}{80} = 5\frac{15}{15} + 1\frac{71}{80} = 6 + 1\frac{71}{80} = 7\frac{71}{80}$$
Ответ: $$7\frac{71}{80}$$
б) $$3\frac{7}{16} - (1\frac{3}{8} + 1\frac{3}{16}) = 3\frac{7}{16} - (1\frac{6}{16} + 1\frac{3}{16}) = 3\frac{7}{16} - 2\frac{9}{16} = 3\frac{7}{16} - 2\frac{9}{16} = 2\frac{23}{16} - 2\frac{9}{16} = \frac{14}{16} = \frac{7}{8}$$
Ответ: $$\frac{7}{8}$$