в) $$9\frac{3}{4} \cdot 10\frac{15}{26} - 10\frac{4}{13} \cdot 9\frac{3}{4} =$$

$$9\frac{3}{4} \cdot 10\frac{15}{26} - 10\frac{4}{13} \cdot 9\frac{3}{4} = 9\frac{3}{4} \cdot (10\frac{15}{26} - 10\frac{4}{13}) = 9\frac{3}{4} \cdot (10 - 10 + \frac{15}{26} - \frac{4}{13}) = 9\frac{3}{4} \cdot (\frac{15}{26} - \frac{4 \cdot 2}{13 \cdot 2}) = 9\frac{3}{4} \cdot (\frac{15}{26} - \frac{8}{26}) = 9\frac{3}{4} \cdot \frac{7}{26} = \frac{9 \cdot 4 + 3}{4} \cdot \frac{7}{26} = \frac{39}{4} \cdot \frac{7}{26} = \frac{3 \cdot 13}{4} \cdot \frac{7}{2 \cdot 13} = \frac{3}{4} \cdot \frac{7}{2} = \frac{21}{8} = 2\frac{5}{8}$$ Ответ: $$2\frac{5}{8}$$