Решение:
а)
\( \frac{3}{4} + \frac{4}{5} = \frac{15+16}{20} = \frac{31}{20} \)
б)
\( \frac{2}{3} + \frac{1}{7} = \frac{14+3}{21} = \frac{17}{21} \)
в)
\( \frac{2}{13} + 0 = \frac{2}{13} \)
г)
\( \frac{5}{9} + \frac{2}{11} = \frac{55+18}{99} = \frac{73}{99} \)
д)
\( \frac{5}{12} + \frac{3}{4} = \frac{5+9}{12} = \frac{14}{12} = \frac{7}{6} \)
е)
\( \frac{5}{6} + \frac{7}{8} = \frac{20+21}{24} = \frac{41}{24} \)
Ответ: а) \( \frac{31}{20} \); б) \( \frac{17}{21} \); в) \( \frac{2}{13} \); г) \( \frac{73}{99} \); д) \( \frac{7}{6} \); е) \( \frac{41}{24} \).