Billy is monitoring the exponential decay of a radioactive compound. He has 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 trepresents 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?