A Machine Is Supposed to Fill Boxes to a Weight $\quad$

A machine is supposed to fill boxes to a weight of 50 pounds. Every 30 minutes a sample of four boxes is tested; the results are given below.
What would be the value of the centerline that would be used in creating an R chart? $\quad$ $\quad$ $\quad$ $\quad$ $\text { Box Weight (Ib) }$
$\begin{array}{|c|cccc|c}\text { Sample }&&&&&\bar{x}\\\hline 1 & 49 & 38 & 39 & 45 & 42.75 \\2 & 52 & 51 & 43 & 61 & 51.75 \\3 & 56 & 60 & 32 & 52 & 50.00 \\4 & 44 & 59 & 46 & 49 & 49.50 \\5 & 51 & 61 & 48 & 45 & 51.25 \\6 & 45 & 50 & 46 & 48 & 47.25 \\7 & 52 & 51 & 45 & 55 & 50.75 \\8 & 40 & 50 & 53 & 48 & 47.75 \\9 & 48 & 67 & 60 & 51 & 56.50 \\10 & 43 & 50 & 50 & 47 & 47.50 \\11 & 48 & 30 & 38 & 39 & 38.75 \\12 & 50 & 46 & 48 & 53 & 49.25 \\13 & 50 & 58 & 56 & 64 & 57.00 \\14 & 47 & 52 & 47 & 49 & 48.75 \\15 & 52 & 57 & 58 & 52 & 54.75\end{array}$

A) $49.567 \text { pounds }$
B) $50 \text { pounds }$
C) $11.000 \text { pounds }$
D) $12.8000\text { pounds }$