A quality analyst wants to construct a control chart for determining whether three machines, all producing the same product, are in control with regard to a particular quality variable. Accordingly, he sampled four units of output from each machine, with the following results:

Machine Measurements

#$117151517$

#$216251825$

#$323242322$

What is the sample mean for machine #$1?$

Multiple Choice

$16$

$21$

$15$

$23$

$17$