3. \(\left(\frac{2}{5}+\frac{13}{15}\right)\cdot6\)

Приведём дроби к общему знаменателю: \(\frac{2}{5}=\frac{6}{15}\).

\(\left(\frac{6}{15}+\frac{13}{15}\right)\cdot6=\frac{19}{15}\cdot6=\frac{38}{5}=7.6\).

Ответ: \(\frac{38}{5}\)