J.R. S. answered • 05/18/18

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fraction remaining = 0.5

^{n}where n = number of half lives that have elapsed (assuming a first order decay)n = 30 hours/14 hours = 2.14 half lives

fraction remaining = 0.5

^{2.14}fraction remaining = 0.2269

mg remaining = 0.2269 x 140 mg = 31.8 mg (to 3 significant figures)