A post office is operated by two clerks. Presume that when Mr. Smith enters the system he discovers that Mr. Jones is being aided by one clerk and Mr. Brown is being served by the other. Supposing that Mr. Smith's service will instigate as soon as one of the clerks is free. If the amount of time that a clerk devotes with any custom is exponentially distributed with mean m, what is the likelihood that, of the three customers, Mr. Smith is the last to leave the post office?