б) ($$\frac{7}{10} + \frac{3}{5}$$) × 15 =

б) ($$\frac{7}{10} + \frac{3}{5}$$) × 15 = ($$\frac{7}{10} + \frac{3 \cdot 2}{5 \cdot 2}$$) × 15 = ($$\frac{7}{10} + \frac{6}{10}$$) × 15 = $$\frac{13}{10} \cdot 15 = \frac{13 \cdot 15}{10} = \frac{13 \cdot 3}{2} = \frac{39}{2} = 19\frac{1}{2} = 19,5$$

Ответ: 19,5