3. 14:15 = 26:x

Решение:

1. \[ 14 : 15 = 26 : x \]
2. \[ x = \frac{15 \times 26}{14} \]
3. \[ x = \frac{390}{14} \]
4. \[ x = \frac{195}{7} \]

Ответ: x = 195/7