AnderSet Laboratories produces rough lenses that will ultimately be ground into precision lenses for use in laboratory equipment. The company has developed the following thickness measures, based on 15 samples of four lenses that were taken when the process was under control: \begin{tabular}{ccc} \hline \begin{tabular}{c} Mean (Microns) \\ (N=4) \end{tabular} & Minimum & Maximum \\ \hline 3.801 & 3.634 & 3.967 \\ 4.087 & 3.885 & 4.283 \\ 4.086 & 4.071 & 4.301 \\ 3.833 & 3.707 & 3.919 \\ 3.991 & 3.527 & 4.056 \\ 4.122 & 3.568 & 4.536 \\ 3.928 & 2.997 & 3.953 \\ 5.215 & 3.778 & 5.682 \\ 4.155 & 2.884 & 4.291 \\ 5.234 & 5.165 & 6.325 \\ 4.228 & 4.051 & 4.246 \\ 4.248 & 3.943 & 4.332 \\ 4.265 & 3.998 & 4.342 \\ 3.739 & 3.638 & 3.835 \\ 4.249 & 4.032 & 4.288 \\ \hline \end{tabular} \begin{tabular}{cccc} \hline \begin{tabular}{c} Sample \\ Size N \end{tabular} & A2 & D3 & D4 \\ \hline 2 & 1.88 & 0 & 3.27 \\ 3 & 1.02 & 0 & 2.57 \\ 4 & 0.73 & 0 & 2.28 \\ 5 & 0.58 & 0 & 2.11 \\ 6 & 0.48 & 0 & 2.00 \\ 7 & 0.42 & 0.08 & 1.92 \\ 8 & 0.37 & 0.14 & 1.86 \\ 9 & 0.34 & 0.18 & 1.82 \\ 10 & 0.31 & 0.22 & 1.78 \\ 11 & 0.29 & 0.26 & 1.74 \\ 12 & 0.27 & 0.28 & 1.72 \\ \hline \end{tabular} a. X is (Enter your response rounded to three decimal places.)