You are using the following procedure from your lab instructions to determine the copper content of a brass sample:
"Approximately 35 mg of a dried brass sample (accurately measured) is put into a 250-mL Erlenmeyer flask. About 20 mL of H2O and 10 mL of concentrated HNO3 is added. This sample is digested, then quantitatively transferred to a 100-mL volumetric flask and diluted to the mark. The sample is still too concentrated, so a 1:20 dilution is accomplished by transferring 5.00 mL of this solution to another 100-mL volumetric flask and diluting to the mark."
If you actually used a 39.5 mg sample of brass, and the resulting diluted solution was found to contain 13.6 mg/L of Cu, what is the %Cu in the sample?