1) 2x = 18 - x; 2) 7x + 3 = 30 - 2x; 3) 7 - 2x = 3x - 18;

Решение:

1. \( 2x = 18 - x \)
   \( 2x + x = 18 \)
   \( 3x = 18 \)
   \( x = \frac{18}{3} \)
   \( x = 6 \)
2. \( 7x + 3 = 30 - 2x \)
   \( 7x + 2x = 30 - 3 \)
   \( 9x = 27 \)
   \( x = \frac{27}{9} \)
   \( x = 3 \)
3. \( 7 - 2x = 3x - 18 \)
   \( 7 + 18 = 3x + 2x \)
   \( 25 = 5x \)
   \( x = \frac{25}{5} \)
   \( x = 5 \)

Ответ: 1) x = 6; 2) x = 3; 3) x = 5.