Решение:

1) $$3\frac{11}{16} - 1\frac{1}{8} = 3\frac{11}{16} - 1\frac{2}{16} = (3-1) + (\frac{11}{16} - \frac{2}{16}) = 2 + \frac{9}{16} = 2\frac{9}{16}$$

2) $$8\frac{5}{12} - 6\frac{7}{20} = 8\frac{25}{60} - 6\frac{21}{60} = (8-6) + (\frac{25}{60} - \frac{21}{60}) = 2 + \frac{4}{60} = 2 + \frac{1}{15} = 2\frac{1}{15}$$

3) $$4\frac{2}{7} - 1\frac{4}{9} = \frac{30}{7} - \frac{13}{9} = \frac{30 \cdot 9}{7 \cdot 9} - \frac{13 \cdot 7}{9 \cdot 7} = \frac{270}{63} - \frac{91}{63} = \frac{179}{63} = 2\frac{53}{63}$$

4) $$8\frac{5}{36} - 1\frac{43}{108} = 8\frac{15}{108} - 1\frac{43}{108} = 7\frac{123}{108} - 1\frac{43}{108} = (7-1) + (\frac{123}{108} - \frac{43}{108}) = 6 + \frac{80}{108} = 6 + \frac{20}{27} = 6\frac{20}{27}$$