Odpowiedź :
1)
[tex]5\dfrac{6}{7}-\dfrac{3}{4}=5\dfrac{6\cdot4}{7\cdot4}-\dfrac{3\cdot7}{4\cdot7}=5\dfrac{24}{28}-\dfrac{21}{28}=\boxed{5\frac{3}{28}}\\[/tex]
2)
[tex]7\dfrac{10}{21}+2\dfrac{9}{14}=7\dfrac{10\cdot2}{21\cdot2}+2\dfrac{9\cdot3}{14\cdot3}=7\dfrac{20}{42}+2\dfrac{27}{42}=9\dfrac{47}{42}=\boxed{10\dfrac{5}{42}}\\[/tex]
[tex]5\frac{6}{7} - \frac{3}{4} = \frac{7\ \cdot \ 5\ + \ 6}{7} - \frac{3}{4} = \frac{41}{7} - \frac{3}{4} = \frac{164}{28} - \frac{21}{28} = \frac{143}{28} = \boxed{5\frac{3}{28}}[/tex]
[tex]7\frac{10}{21} + 2\frac{9}{14} = \frac{21\ \cdot \ 7\ + \ 10}{21} + \frac{14\ \cdot \ 2\ + \ 9}{14} = \frac{157}{21} + \frac{37}{14} = \frac{314}{42}+ \frac{111}{42} = \frac{425}{42} = \boxed{10\frac{5}{42}}[/tex]