А: 1) 2/7 + 11/21 + 321/49; 2) (1/2 + 2/7) · 14/13; 3) (3/4 + 7/5) · 0,7 : 86/17.

1. Приведём дроби к общему знаменателю 147:

   \(\frac{2}{7}+\frac{11}{21}+\frac{321}{49}=\frac{42}{147}+\frac{77}{147}+\frac{963}{147}=\frac{1082}{147}\).

2. \(\left(\frac{1}{2}+\frac{2}{7}\right)\cdot\frac{14}{13}=\frac{11}{14}\cdot\frac{14}{13}=\frac{11}{13}\).

3. \(0,7=\frac{7}{10}\).

   \(\left(\frac{3}{4}+\frac{7}{5}\right)\cdot0,7:\frac{86}{17}=\frac{43}{20}\cdot\frac{7}{10}\cdot\frac{17}{86}=\frac{301}{200}\cdot\frac{17}{86}=\frac{119}{400}\).

Ответ: 1) \(\frac{1082}{147}\); 2) \(\frac{11}{13}\); 3) \(\frac{119}{400}\).