1) $$7\cdot 2\frac{6}{7}=7\cdot (2+\frac{6}{7})=7\cdot 2 + 7\cdot \frac{6}{7}=14+6=20$$
2) $$10\cdot 1\frac{5}{8}=10\cdot (1+\frac{5}{8})=10\cdot 1 + 10\cdot \frac{5}{8}=10+\frac{50}{8}=10+\frac{25}{4}=10+6\frac{1}{4}=16\frac{1}{4}$$
3) $$8\cdot 7\frac{3}{8}=8\cdot (7+\frac{3}{8})=8\cdot 7 + 8\cdot \frac{3}{8}=56+3=59$$
4) $$3\cdot 5\frac{5}{9}=3\cdot (5+\frac{5}{9})=3\cdot 5 + 3\cdot \frac{5}{9}=15+\frac{15}{9}=15+\frac{5}{3}=15+1\frac{2}{3}=16\frac{2}{3}$$
Ответ: 1) 20; 2) 16$$\frac{1}{4}$$; 3) 59; 4) 16$$\frac{2}{3}$$.