Решение:
a) $$6\frac{15}{21}+2\frac{9}{14} = 6\frac{5}{7}+2\frac{9}{14} = 6\frac{10}{14}+2\frac{9}{14} = 8\frac{19}{14} = 9\frac{5}{14}$$
б) $$5\frac{1}{6}-3\frac{3}{4} = 5\frac{2}{12}-3\frac{9}{12} = 4\frac{14}{12}-3\frac{9}{12} = 1\frac{5}{12}$$
в) $$3\frac{3}{5} \cdot 1\frac{1}{9} = \frac{18}{5} \cdot \frac{10}{9} = \frac{2}{1} \cdot \frac{2}{1} = 4$$
г) $$1\frac{3}{7}:14 = \frac{10}{7}:14 = \frac{10}{7} \cdot \frac{1}{14} = \frac{5}{49}$$
д) $$48:\frac{12}{13} = \frac{48}{1} \cdot \frac{13}{12} = \frac{4}{1} \cdot \frac{13}{1} = 52$$
e) $$\frac{15}{16}:5 = \frac{15}{16} \cdot \frac{1}{5} = \frac{3}{16}$$
Ответ: a) $$9\frac{5}{14}$$, б) $$1\frac{5}{12}$$, в) $$4$$, г) $$\frac{5}{49}$$, д) $$52$$, e) $$\frac{3}{16}$$