Chapter 6.1, Problem 48ES

The accompanying figure shows the rate at which transdermal medication is absorbed into the bloodstream of an individual, as well as the rate at which the medication is eliminated from the bloodstream by metabolization. Both rates are in units of micrograms per hour $\left(\mu g/h\right)$ and are displayed over an $8\text{-hour}$ period. What does the area $A$ between the curves over the interval $\left[0,8\right]$ represent? Justify your answer.