в)11$$\frac{21}{28}$$-9$$\frac{12}{28}$$+$$\frac{1}{28}$$;

в) 11$$\frac{21}{28}$$-9$$\frac{12}{28}$$+$$\frac{1}{28}$$ = (11 - 9) + ($$\frac{21}{28}$$ - $$\frac{12}{28}$$ + $$\frac{1}{28}$$) = 2 + $$\frac{21 - 12 + 1}{28}$$ = 2 + $$\frac{10}{28}$$ = 2 + $$\frac{5}{14}$$ = 2$$\frac{5}{14}$$

Ответ: 2$$\frac{5}{14}$$