33) x/21 = 8 - x/7 34) x/30 = 4 - x/6 35) x/12 - 5 = -x/18

Решение:

• 33. \(\frac{x}{21} = 8 - \frac{x}{7}\)
  Умножим обе части на 21:
  \[ 21 \times \frac{x}{21} = 21 \times 8 - 21 \times \frac{x}{7} \]
  \[ x = 168 - 3x \]
  \[ x + 3x = 168 \]
  \[ 4x = 168 \]
  \[ x = \frac{168}{4} = 42 \]
• 34. \(\frac{x}{30} = 4 - \frac{x}{6}\)
  Умножим обе части на 30:
  \[ 30 \times \frac{x}{30} = 30 \times 4 - 30 \times \frac{x}{6} \]
  \[ x = 120 - 5x \]
  \[ x + 5x = 120 \]
  \[ 6x = 120 \]
  \[ x = \frac{120}{6} = 20 \]
• 35. \(\frac{x}{12} - 5 = -\frac{x}{18}\)
  Умножим обе части на 36 (наименьшее общее кратное 12 и 18):
  \[ 36 \times \frac{x}{12} - 36 \times 5 = -36 \times \frac{x}{18} \]
  \[ 3x - 180 = -2x \]
  \[ 3x + 2x = 180 \]
  \[ 5x = 180 \]
  \[ x = \frac{180}{5} = 36 \]

Ответ: 33) \(x = 42\); 34) \(x = 20\); 35) \(x = 36\)