Billy is monitoring the exponential decay of a radioactive

Last updated: 7/21/2022

Billy is monitoring the exponential decay of a radioactive compound. He has a sample of the compound in a test tube in his lab. According to his calculations, the sample is decaying at a rate of 35% per hour. There are at least 72 grams of the sample remaining. Once the sample reaches a mass of 15 grams, Billy will continually add more of the compound to keep the sample size at a minimum of 15 grams. If R represents the actual amount of the sample remaining, in grams, and t represents the time in hours, then which of the following systems of inequalities can be used to determine the possible mass of the radioactive sample over time?