a) $$\frac{3}{4} \cdot 2 = \frac{3 \cdot 2}{4} = \frac{6}{4} = \frac{3}{2} = 1\frac{1}{2}$$
б) $$\frac{9}{12} \cdot 4 = \frac{9 \cdot 4}{12} = \frac{3 \cdot 4}{4} = 3$$
в) $$\frac{7}{15} \cdot 15 = \frac{7 \cdot 15}{15} = 7$$