3.12; 9

$$3\frac{1}{9} \cdot 12 = \frac{3 \cdot 9 + 1}{9} \cdot 12 = \frac{28}{9} \cdot 12 = \frac{28 \cdot 12}{9} = \frac{336}{9} = 37 \frac{3}{9} = 37 \frac{1}{3}$$.

Ответ: $$37 \frac{1}{3}$$.