Ответ:

[tex]\frac{5}{6}[/tex] - [tex]\frac{21}{42}[/tex] = [tex]\frac{35}{42}[/tex] - [tex]\frac{21}{42}[/tex] = [tex]\frac{14}{42}[/tex].

14: [tex]\frac{14}{42}[/tex] = [tex]\frac{1}{3}[/tex].