A scientist is observing a sample of a radioactive substance. The table below shows the amount of the radioactive substance remaining, in milligrams, with respect to time, in hours, since the scientist began observing the sample. Time (hours) 1 2 3 4 5 Amount Remaining (milligrams) 288 144 72 36 18 The independent variable in the relationship is the and should be placed on the . The dependent variable in the relationship is the and should be placed on the .