Chemistry
posted by Alex .
A deceased person is found by the coronoer to have a cocaine concentration of 50 ng/dL. What is the concentration of cocaine in his blood two hours earlier?

What is the rate? You must have that in your information somewhere.

rate is 1.1 ng/dLhr

Is this a first order reaction? If so then
ln(No/N) = kt
Substitute No and solve for it.
N = 50
k = 1.1
t = 2.
If this is not a first order decay please repost giving ALL of the information in the problem.