19. 2x-4 = 3/7

Решение:

1. \[ 2x - 4 = \frac{3}{7} \]
2. \[ 2x = \frac{3}{7} + 4 \]
3. \[ 2x = \frac{3}{7} + \frac{28}{7} \]
4. \[ 2x = \frac{31}{7} \]
5. \[ x = \frac{31}{7 \times 2} \]
6. \[ x = \frac{31}{14} \]

Ответ: x = 31/14