Respuesta :

Annder

Step-by-step explanation:

1. 2x + 21 = 40

2x = 40 - 21

2x = 19

x = 19/2 = 9.5

2. 4x - 12 = 3x + 9

4x - 3x = 9 + 12

x = 21

3. 3x - 3 + 2 = 7x

3x - 1 = 7x

-1 = 7x - 3x

-1 = 4x

4x = -1

x = -1/4

= - 0.25

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