Percentage of Copper in Brass Screw

Hamza conducts an experiment to find how much copper is in a typical brass screw. Hamza thinks about how Beer's law can help find his concentration, but for that he needs a solution.He first weighs his brass screw and obtains a mass of $.7841 \text{g}$ . He then proceeds to dissolve the brass screw with an oxiding agent in the reaction $\text{Cu}(s)+ 4\text{HNO}_3(aq) \rightarrow \text{ Cu(NO}_3)_2(aq) +2\text{NO}_2(g)+2\text{H}_2\text{O}(l)$

Hamza then dilutes the Copper Nitrate solution using a $100 \text{mL}$ volumetric flask. He measures the solutions' absorbance and obtains an absorbance of $.228$ . He sets his calibration curve for $\text{ Cu(NO}_3)_2(aq)$ and obtains an equation $A=1.294c+.1400$

Given the data above, find the percentage of copper in the brass screw.