б) 1/4 * 72 + 3/4 * 72= — 6 + 6+2

б) $$\frac{\frac{1}{4} \cdot 72 + \frac{3}{4} \cdot 72}{6 + 6 + 2} = \frac{\frac{1}{4} \cdot 72 + \frac{3}{4} \cdot 72}{14} = \frac{18 + 54}{14} = \frac{72}{14} = \frac{36}{7} = 5 \frac{1}{7}$$

Ответ: 5 1/7