3. \(\left(\frac{1}{5}+\frac{8}{15}\right)\cdot6\)

Приведём дроби в скобках к знаменателю 15:

\(\left(\frac{3}{15}+\frac{8}{15}\right)\cdot6=\frac{11}{15}\cdot6=\frac{66}{15}=\frac{22}{5}\).

Ответ: \(\frac{22}{5}\).