An endocrine$-$disrupting chemical was determined by UV$-$Vis spectrophotometry and standard addition method. For the addition, $100\mathrm{.}0$ uL of a $1000\mathrm{.}0$ ug$/$mL standard was added to $100\mathrm{.}0$ mL of solution. The following data were obtained:

Absorbance of reagent blank $=0\mathrm{.}020$

Absorbance of sample $=0\mathrm{.}540$

Absorbance of sample plus spike $=1\mathrm{.}040$

Calculate the concentration of the sample in ug$/$mL