The concentration of a drug in the bloodstream

Question

The concentration of a drug in the bloodstream tt hours after injection is given by the function C(t)=0.7te−1.5t,Ct=0.7te-1.5t, where the concentration is measured in milligrams/meter. How fast is the concentration changing in 1.5 hours. Round your answer to three decimal places and write out units using / to represent per.

The answer is not -0.092 which is what I have been getting

Answer 1

C'(t) = -1.05e^-1.5t

Substitute 1.5 for t and simplfy

Answer 2

Rate of change of concentration is d(C(t))/dt = d(0.7te^-1.5t)/dt = 0.7 * (e^-1.5t + t*-1.5e^-1.5t) = (0.7-1.05t)e^-1.5t

Rate of change of concentration at 1.5 hours = (0.7-1.05*1.5)e^-1.5*1.5 = -0.0922