3. \(\left(\frac{2}{9}+1\frac{9}{12}\right)\cdot 7{,}2\)

Сократим дробь и преобразуем десятичную дробь:

\(1\frac{9}{12}=1\frac{3}{4}=\frac{7}{4}\), \(7{,}2=\frac{36}{5}\).

\(\left(\frac{2}{9}+\frac{7}{4}\right)\cdot\frac{36}{5}=\left(\frac{8}{36}+\frac{63}{36}\right)\cdot\frac{36}{5}=\frac{71}{36}\cdot\frac{36}{5}=\frac{71}{5}=14{,}2\).

Ответ: 14,2.