б) 3. (6 + a) = 45 12- 40: y = 4 (30-n) : 2 = 9 3-b-15 = 6 14 + (c - 8) = 31

Решим уравнения и сделаем проверку.

3 ⋅ (6 + a) = 45

6 + a = 45 : 3

6 + a = 15

a = 15 - 6

a = 9

Проверка:

3 ⋅ (6 + 9) = 45

3 ⋅ 15 = 45

45 = 45

Ответ: a = 9

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12 - 40 : y = 4

-40 : y = 4 - 12

-40 : y = -8

y = -40 : (-8)

y = 5

Проверка:

12 - 40 : 5 = 4

12 - 8 = 4

4 = 4

Ответ: y = 5

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(30 - n) : 2 = 9

30 - n = 9 ⋅ 2

30 - n = 18

-n = 18 - 30

-n = -12

n = 12

Проверка:

(30 - 12) : 2 = 9

18 : 2 = 9

9 = 9

Ответ: n = 12

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3 ⋅ b - 15 = 6

3 ⋅ b = 6 + 15

3 ⋅ b = 21

b = 21 : 3

b = 7

Проверка:

3 ⋅ 7 - 15 = 6

21 - 15 = 6

6 = 6

Ответ: b = 7

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14 + (c - 8) = 31

c - 8 = 31 - 14

c - 8 = 17

c = 17 + 8

c = 25

Проверка:

14 + (25 - 8) = 31

14 + 17 = 31

31 = 31

Ответ: c = 25