Задание 4 1. (21+x) * 3 - 54 : 9 = 45 2. 63 : x - 9 + 12 * 3 = 30 3. (16-x): 2 * 6 + 18 = 42 4. 9 * x + 72:8-21 = 0

1. (21+x) * 3 - 54 : 9 = 45

(21 + x) * 3 - 6 = 45

(21 + x) * 3 = 45 + 6

(21 + x) * 3 = 51

21 + x = 51 : 3

21 + x = 17

x = 17 - 21

x = -4

Ответ: -4

2. 63 : x - 9 + 12 * 3 = 30

63 : x - 9 + 36 = 30

63 : x + 27 = 30

63 : x = 30 - 27

63 : x = 3

x = 63 : 3

x = 21

Ответ: 21

3. (16-x): 2 * 6 + 18 = 42

(16 - x) : 2 * 6 + 18 = 42

(16 - x) : 2 * 6 = 42 - 18

(16 - x) : 2 * 6 = 24

(16 - x) : 2 = 24 : 6

(16 - x) : 2 = 4

16 - x = 4 * 2

16 - x = 8

x = 16 - 8

x = 8

Ответ: 8

4. 9 * x + 72 : 8 - 21 = 0

9 * x + 9 - 21 = 0

9 * x - 12 = 0

9 * x = 12

$$x = \frac{12}{9} = \frac{4}{3} = 1\frac{1}{3}$$

Ответ: $$\frac{4}{3}$$ или $$1\frac{1}{3}$$