You received a job in a company that recycles Li batteries. You are analyzing the Li solutions by flame emission. The matrix of the batteries is quite complex and the spike recoveries keep failing. The Li concentration was determined by atomic emission using the method of standard additions.

To each the five $(5)100\mathrm{.}0$ mL flask $7\mathrm{.}8$ mL of Li$-$bearing battery solution$/$sample was added. Aliquots of a $1\mathrm{.}62$ mg$/$L Li standard solution was added to each flask, see table below. Each flask was diluted to the mark with DI water.

From the data and the following graph, find the concentration of Li in the unknown Li$-$bearing battery solution$/$sample in ppm$.$ Report your answer to $3$ decimal points and no units.

$\backslash$table$[[\backslash$table$[[$Vol of $1\mathrm{.}62$ mg$/$L Li$],[$Standard$]],$Total Volume,Pe $($signal$)],[mL,mL,$arbitarty Units$],[0\mathrm{.}00,100\mathrm{.}0,309],[5\mathrm{.}00,100\mathrm{.}0,452],[10\mathrm{.}00,100\mathrm{.}0,600],[15\mathrm{.}00,100\mathrm{.}0,765],[20\mathrm{.}00,100\mathrm{.}0,906]]$