The concentration c (in mg/dl), of a certain antibiotic in a patient's bloodstream is given by c(t)=50 t /(t^2 + 25)  where t is the time (in hours) after taking the antibiotic. what is the concentration 5 hours after taking the antibiotic?

Given that the concentration has been modeled by the formula:
C(t)=50t/(t^2+25)
where:
t is time in hours.
The concentration after 5 hours will be given by:
t= 5 hours 
plugging the value in the equation we get:
C(5)=(50(5))/(5^2+25)
simplifying the above we get:
C(5)=250/(50)=5 mg/dl

5 mg/dl