- 7 * 3 + 7 * 2 * x = - 6 * x - 1 ;

- 21 + 14 * x = - 6 * x - 1

14 * x + 6 * x = - 1 + 21 ;

x * ( 14 + 6 ) = 21 - 1

20 * x = 20

x = 20 / 20

x = 1