b$.$ Sort by $x_1,$ then by $x_2,$ then by $x_3,$ and then by $x_4$ all in ascending order. Note that all variables are sorted simultaneously. What are the $x_1,x_2,x_3,$ and $x_4$ values of the first observation after the data are sorted? $($For $x_1,$ round your answer to four decimal places.$)$