Resposta :

5x - 3 + x = 2x + 9
5x + x - 2x = 9 + 3
4x = 12
x = 12 : 4
x = 3
5x - 3 + x = 2x + 9
5x + x - 2x = + 9 + 3
6x - 2x = 12
4x = 12
x = 12
       4
x = 3
Confirmando:
5 * 3 - 3 + 3 = 15
2 * 3 + 9 = 15

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