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 an exponential random variable $x$ with $=0\mathrm{.}40.$

Suppose a randomly selected document is sent to the main printer.

$($a$)$ What is the mean time, $,$ until the document begins to print? Give your answer in minutes to one decimal place.