$,$ In the Gensler Architectural firm, all of the computers are part of a local area network, connected to one main printer. When an$,$architect prints a document, the job is placed in a queue. It may take several minutes before the document begins to print, due to the number of other print jobs and the complexity of the document. The time $($in minutes$)$ until the document starts to print is anexponential random variable X with $1=0\mathrm{.}40.$Suppose a randomly selected document is sent to the main printer.$($a$)$ What is the mean time, u$,$ until the document begins to print? Give your answer in minutes to one decimal place.