а) (5/12 + 1/3)·3

\( \left( \frac{5}{12} + \frac{1}{3} \right) \cdot 3 = \left( \frac{5}{12} + \frac{4}{12} \right) \cdot 3 = \frac{9}{12} \cdot 3 = \frac{9}{4} \cdot 3 = \frac{27}{4} \approx 6,75 \)