3. Решите пропорцию: a) \frac{x}{24}=\frac{3}{28}; б) x: 13 = 24:39.

а) $$ \frac{x}{24}=\frac{3}{28} $$

$$ x = \frac{24 \cdot 3}{28} $$

$$ x = \frac{72}{28} $$

$$ x = \frac{18}{7} = 2\frac{4}{7} $$

б) $$ x: 13 = 24:39 $$

$$ \frac{x}{13} = \frac{24}{39} $$

$$ x = \frac{24 \cdot 13}{39} $$

$$ x = \frac{312}{39} $$

$$ x = 8 $$

Ответ: а) $$2\frac{4}{7}$$; б) 8