Officials are testing athletes for doping at a sporting event. They model the concentration of a particular drug in an athlete’s bloodstream using the equation D = 6 e^{−t /10} where D is the concentration of the drug in mg/l and t is the time in hours since the athlete took the drug.

a. Interpret the meaning of the constant 6 in this model.

b. Find the concentration of the drug in the bloodstream after 2 hours.

c. It is impossible to detect this drug in the bloodstream if the concentration is lower than 3 mg/l. Show that this happens after t = −10 ln (1/2) and convert this result into hours and minutes.