Answer :

choixongdong

Answer:

12

Step-by-step explanation:

20x^2 + 160 = 400 + 220x

20x^2 - 220x - 240 = 0

20(x^2 - 11x - 12) = 0

20(x - 12)(x + 1) = 0

x - 12 = 0; x = 12

x + 1 = 0; x = - 1. (can't be negative)

So answer is 12 hours

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