Find the sum 2 3/7 + 3 2/21 + 2 2 1/5 + 4 2/3 + 3 3/4 5/7 + 6 + 4 2/5

$$\frac{17}{7} = \frac{17 \times 3}{7 \times 3} = \frac{51}{21}$$ $$\frac{2}{1} = \frac{2 \times 21}{1 \times 21} = \frac{42}{21}$$

$$\frac{125}{21} = 5\frac{20}{21}$$

अतः, उत्तर है: $\boxed{\mathbf{5\frac{20}{21}}}$

2) $2\frac{1}{5} + 4\frac{2}{3} + 3\frac{3}{4}$

$$2\frac{1}{5} = \frac{(2 \times 5) + 1}{5} = \frac{11}{5}$$ $$4\frac{2}{3} = \frac{(4 \times 3) + 2}{3} = \frac{14}{3}$$ $$3\frac{3}{4} = \frac{(3 \times 4) + 3}{4} = \frac{15}{4}$$

$$\frac{11}{5} = \frac{11 \times 12}{5 \times 12} = \frac{132}{60}$$ $$\frac{14}{3} = \frac{14 \times 20}{3 \times 20} = \frac{280}{60}$$ $$\frac{15}{4} = \frac{15 \times 15}{4 \times 15} = \frac{225}{60}$$

$$\frac{637}{60} = 10\frac{37}{60}$$

अतः, उत्तर है: $\boxed{\mathbf{10\frac{37}{60}}}$

3) $\frac{5}{7} + 6 + 4\frac{2}{5}$

$$\frac{5}{7} = \frac{5 \times 5}{7 \times 5} = \frac{25}{35}$$ $$\frac{6}{1} = \frac{6 \times 35}{1 \times 35} = \frac{210}{35}$$ $$\frac{22}{5} = \frac{22 \times 7}{5 \times 7} = \frac{154}{35}$$

$$\frac{389}{35} = 11\frac{4}{35}$$

अतः, उत्तर है: $\boxed{\mathbf{11\frac{4}{35}}}$