Please show how the answer is 34.1

The information below includes results from a clinical study evaluating the pharmacokinetics of a test compound (LIU323) after the administration of an IV bolus dose to a healthy human volunteer. Dose =4.5mg Cmax =34.0ng/mL Elimination half-life =7.5hr Assuming the MEC is 10.0ug/L, how long would the medication be effective following administration of a 31.0mg dose? Answer: 22(34.1)