12-4(x-3)=39-9x 3x=28-x 5x+12=8x+30 -7(2-3x)=56 (5+7a)*15=-30

1) 12 - 4 * (x - 3) = 39 - 9 * x;

- 4 * (x - 3) + 9 * x = 39 - 12;

- 4 * x + 4 * 3 + 9 * x = 39 - 12;

9 * x - 4 * x = 27 - 4 * 3;

5 * х = 27 - 12;

5 * х = 15;

х = 15/5;

х = 3.

2) 3 * x = 28 - x;

3 * x + x = 28;

4 * х = 28;

х = 28/4;

х = 7.

3) 5 * x + 12 = 8 * x + 30;

5 * x - 8 * x = 30 - 12;

- 3 * х = 18;

х = - 18 : 3;

х = - 6.

4) - 7 * (2 - 3 * x) = 56;

- 7 * 2 + 7 * 3 * x = 56;

21 * х = 56 + 7 * 2;

21 * х = 56 + 14;

21 * х = 70;

х = 70/21;

х = 10/3;

х = 3 1/3.

5) (5 + 7 * a) * 15 = - 30;

75 + 105 * а = - 30;

105 * а = - 30 - 75;

105 * а = - 105;

а = - 105/105;

а = - 1.