4) 4\frac{7}{12} - (-1\frac{3}{11}) - (-1\frac{13}{15}) - (-1\frac{45}{64}); 5) \frac{81}{88} - (-6 + \frac{13}{15}) - (-1\frac{19}{21}); 6) (- \frac{4}{5} - \frac{7}{7}) \cdot (5\frac{7}{11} - \frac{12}{12})

4) 4\frac{7}{12} - (-1\frac{3}{11}) - (-1\frac{13}{15}) - (-1\frac{45}{64}) = \frac{55}{12} + \frac{14}{11} + \frac{28}{15} + \frac{109}{64} = \frac{55 \cdot 11 \cdot 15 \cdot 64 + 14 \cdot 12 \cdot 15 \cdot 64 + 28 \cdot 12 \cdot 11 \cdot 64 + 109 \cdot 12 \cdot 11 \cdot 15}{12 \cdot 11 \cdot 15 \cdot 64} = \frac{577920 + 161280 + 234432 + 215820}{126720} = \frac{1189452}{126720} = 9,38

5) \frac{81}{88} - (-6 + \frac{13}{15}) - (-1\frac{19}{21}) = \frac{81}{88} + 6 - \frac{13}{15} + 1 + \frac{19}{21} = \frac{81}{88} + 7 - \frac{13}{15} + \frac{19}{21} = \frac{81 \cdot 15 \cdot 21 + 7 \cdot 88 \cdot 15 \cdot 21 - 13 \cdot 88 \cdot 21 + 19 \cdot 88 \cdot 15}{88 \cdot 15 \cdot 21} = \frac{25515 + 194040 - 24264 + 24880}{27720} = \frac{220171}{27720} = 7,94

6) (- \frac{4}{5} - \frac{7}{7}) \cdot (5\frac{7}{11} - \frac{12}{12}) = (-\frac{4}{5} - 1) \cdot (5\frac{7}{11} - 1) = (-\frac{4}{5} - \frac{5}{5}) \cdot (\frac{62}{11} - 1) = -\frac{9}{5} \cdot \frac{51}{11} = -\frac{459}{55} = -8,34