Respuesta :

melatleul

Answer:

-9

Step-by-step explanation:

let 'x' be the unknown number

lets change the statment to an equation

8x + 3x = 12x + 9

11x = 12x + 9

11x-12x = 9

-x = 9

x = -9

hope it helps ❤❤❤

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