a) $$7 - 4\frac{5}{9} = 6\frac{9}{9} - 4\frac{5}{9} = 2\frac{4}{9}$$
б) $$4\frac{3}{10} + 1\frac{1}{12} = 4\frac{18}{60} + 1\frac{5}{60} = 5\frac{23}{60}$$
в) $$6\frac{13}{21} + 2\frac{9}{14} = 6\frac{26}{42} + 2\frac{27}{42} = 8\frac{53}{42} = 9\frac{11}{42}$$
Ответ: a) $$2\frac{4}{9}$$; б) $$5\frac{23}{60}$$; в) $$9\frac{11}{42}$$