Marie is logging the number of radioactive isotopes she observes every minute. She has determined her function to be f (x) = - 4x + 120. Based on the situation, describe any necessary restrictions to the domain and range and provide justification or the restrictions

If f (x) represents the # of radioactive isotopes present, then f (x) must always be 120 or less, down to zero. f (x) is zero when x = 30. Thus, the range is [0,120], and the domain is [0,30]. The domain represents time measurements; we assume we begin at x=0, and then determine at what value of x the function f (x) will reach zero.