J.R. S. answered • 05/18/18

Ph.D. in Biochemistry--University Professor--Chemistry Tutor

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)