12) \(\left(\dfrac{2}{5}+\dfrac{13}{15}\right)\cdot 6\)

Приведём дроби к общему знаменателю 15:

\(\dfrac{2}{5}=\dfrac{6}{15}\).

\(\left(\dfrac{2}{5}+\dfrac{13}{15}\right)\cdot 6=\left(\dfrac{6}{15}+\dfrac{13}{15}\right)\cdot 6=\dfrac{19}{15}\cdot 6=\dfrac{114}{15}=\dfrac{38}{5}=7\dfrac{3}{5}\).

Ответ: \(7\dfrac{3}{5}\).