Cars arrive randomly at an intersection with an average rate of 20 cars per hour. The likelihood, or probability, that no car enters the intersection within a period of x minutes can be estimated by f(x) = e^-x/3.
(a) What is the likelihood that no car enters the intersection during a 5-minute period? 

(b) Determine the value of x that gives a 30% chance that no car enters the intersection during an interval of x minutes.