Й) $$3\frac{3}{4} \cdot (4\frac{1}{2} : 6\frac{3}{4})$$

Й) $$3\frac{3}{4} \cdot (4\frac{1}{2} : 6\frac{3}{4}) = \frac{15}{4} \cdot (\frac{9}{2} : \frac{27}{4}) = \frac{15}{4} \cdot (\frac{9}{2} \cdot \frac{4}{27}) = \frac{15}{4} \cdot \frac{9 \cdot 4}{2 \cdot 27} = \frac{15}{4} \cdot \frac{36}{54} = \frac{15}{4} \cdot \frac{2}{3} = \frac{15 \cdot 2}{4 \cdot 3} = \frac{30}{12} = \frac{5}{2} = 2\frac{1}{2}$$

Ответ: $$2\frac{1}{2}$$