Drug epidemic in an epidemiological model used to study the spread of drug use, a single drug user is introduced into a population of n non-users. under certain assumptions, the number of people expected to use drugs as a result of direct influence from each drug user is given by
s=∫^[infinity]_0 a(1-e^-kt)/k e^-kt dt.
where a, b and k are constants. find the value of s.