Respuesta :

Answer: the number must be placed in the box is 9

suppose: the number must be placed in the box is x

have:

5u + 3(4u - 6) = -3u -27 + 20u + x

⇔ 5u + 12u - 18 = -3u - 27 + 20u +x

⇔ 17u + 3u - 20u = -27 + 18 + x

⇔ 0 = x - 9

⇔ x = 9

Step-by-step explanation:

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