Ответ: Б, В

1)3х + 7х + 4 х = 280

14х = 280

х = 20

2) 6м + м - 35 = 21

7м = 21 + 35

7м = 56

м = 8

3) 6а + 3а - а = 6400

8а = 6400

а = 800

4) 5n + 9n + 32 = 200

14n = 200 - 32

14n = 168

5) (x + 9) * 4 = 76

4x + 36 = 76

4x = 76-36

4x = 40

x = 10

6) 102m - 4m + 8 =  1968

98 m = 1968 - 8

98m = 1960

m = 20

7) (3 x + 5 x) * 18 = 144

54 x + 90x = 144

144 x = 144

x = 1

8) 4 * x * 8 *3 = 48096

4x = 48096:24

4x = 2004

x = 501

9) 7 * (15y - 7y) = 224

105y - 49y = 224

56y = 224

y = 4

10) 35 * (14 + x) - 476 + 6x = 383

490 + 35 x - 476 + 6x = 383

6x + 35x = 383 + 476 - 490

41 x = 369

x = 9

11) 3 * (2x + 5) + (3x + 9) * 2 + (5x - 4) * 4 = 6577

6x + 15 + 6x + 18 + 20x - 16 = 6577

6x + 6x + 20x = 6577 + 16 - 18 - 15

32 x = 6560

x = 205

12) 144 + (3y - 18) *5 + 4y  = 149

144 + 15y - 90 + 4y = 149

15y + 4y = 149 + 90 - 144

19 y = 95

y = 5

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