Ответ:

  1. \(\frac{18}{35}+\frac{12}{35}=\frac{30}{35}=\frac{6}{7}\).
  2. \(\frac{27}{99}+\frac{9}{99}=\frac{36}{99}=\frac{4}{11}\).
  3. \(\frac{57}{45}-\frac{32}{45}=\frac{25}{45}=\frac{5}{9}\).
  4. \(\frac{69}{72}-\frac{63}{72}=\frac{6}{72}=\frac{1}{12}\).