Question 536330
If cooking time is linearly related to temperature, which is not the case, it's more likely to be related to absolute temps than Fahrenheit.
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350 F = 841 R
250 F = 741 R
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3*841 = t*741
t = 3.4 hours
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If you cook it at 0 F, it'll take 5.13 hours.  Good luck with that.