Решение:
a) $$8.04 \cdot (-3.2) - (-0.18) \cdot (-0.4) = -25.728 - 0.072 = -25.8$$
б) $$\frac{9}{14} \cdot (-2\frac{1}{3}) + (-3\frac{3}{4}) \cdot \frac{5}{6} = \frac{9}{14} \cdot (-\frac{7}{3}) + (-\frac{15}{4}) \cdot \frac{5}{6} = -\frac{9 \cdot 7}{14 \cdot 3} - \frac{15 \cdot 5}{4 \cdot 6} = -\frac{3}{2} - \frac{25}{8} = -\frac{12}{8} - \frac{25}{8} = -\frac{37}{8} = -4\frac{5}{8}$$
Ответ:
a) -25.8
б) -4 5/8