d) A drug decomposes by first-order kinetics with a rate constant of 0.02 month 1. If the initial concentration is 50mgmL1 calculate: i) The shelf-life (t0.9) ii) The half-life (t0.5) iii) The amount of drug remaining after 1 year iv) The time required for the drug concentration to reach 80mgmL1 v) The time required for the drug concentration to reach 60mgmL1