**Question: Let D(t) represent the amount of drug in a patient (measured in grams) at time t (mea- sured in hour). The initial amount of drug is 90 grams. After 2 hours the amount is 70 grams. Assuming that the amount of drug decays exponentially, address the following problems. (a) Write down a differential equation that best describes the growth of the amount of the drug. (b) Find the general solution to the differential equation in part (a). (c) Use the additional provided information to determine D(t). (d) What is the half-life for D(t)?**

**Solution: **