Question 1188373
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t^4 + 6t^3 - t^2 - 6t = factor by grouping = t^3*(t+6) - t*(t+6) = (t^3 - t)*(t+6) = t*(t^2-1)*(t+6).


5220 is divisible by 2 and by 3 (via the sum of digits), so it is divisible by 6.


So, try t = 6, and you will see that  6*(6^2-1)*(6+6) = 6*35*12 = 2520.


So, t= 6 hours is one of possible solutions.
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