The concentration of a certain drug, in mg/L, can be modeled by the following function: C(t)=5t*e-0.8t, where t is the number of hours after the drug was administered. The drug is effective if its concentration is greater than 1.2mg/L. Use the graph of the function to determine the interval of time when the drugs is effective.
A. (0,0.31)
B. (3.26,