The radioactive isotope sodium-24 is used as a tracer to measure the rate of flow in an artery or vein. The half-life of sodium-24 is 14.9 hours. Suppose that a hospital buys a 40-g sample of sodium-24 and will reorder when the sample is reduced to 3 g. a: How much of the sample will remain after 50 hours?.b: How often before the hospital has to reorder sodium-24?c: How much of the sample will remain after 1 year?